<s>
Copyleft	B-License
is	O
the	O
legal	O
technique	O
of	O
granting	O
certain	O
freedoms	O
over	O
copies	O
of	O
copyrighted	O
works	O
with	O
the	O
requirement	O
that	O
the	O
same	O
rights	O
be	O
preserved	O
in	O
derivative	O
works	O
.	O
</s>
<s>
Licenses	O
which	O
implement	O
copyleft	B-License
can	O
be	O
used	O
to	O
maintain	O
copyright	O
conditions	O
for	O
works	O
ranging	O
from	O
computer	B-Application
software	I-Application
,	O
to	O
documents	O
,	O
art	O
,	O
scientific	O
discoveries	O
and	O
even	O
certain	O
patents	O
.	O
</s>
<s>
Copyleft	B-License
software	B-License
licenses	I-License
are	O
considered	O
protective	O
or	O
reciprocal	O
in	O
contrast	O
with	O
permissive	B-License
free	I-License
software	I-License
licenses	I-License
,	O
and	O
require	O
that	O
information	O
necessary	O
for	O
reproducing	O
and	O
modifying	O
the	O
work	O
must	O
be	O
made	O
available	O
to	O
recipients	O
of	O
the	B-Application
software	I-Application
program	O
,	O
which	O
are	O
often	O
distributed	O
as	O
binary	B-Application
executables	I-Application
.	O
</s>
<s>
Notable	O
copyleft	B-License
licenses	I-License
include	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
(	O
GPL	B-License
)	O
,	O
originally	O
written	O
by	O
Richard	O
Stallman	O
,	O
which	O
was	O
the	O
first	O
software	B-Application
copyleft	B-License
license	I-License
to	O
see	O
extensive	O
use	O
,	O
the	O
Mozilla	B-License
Public	I-License
License	I-License
,	O
the	O
Free	B-Application
Art	O
License	O
,	O
and	O
the	O
Creative	O
Commons	O
share-alike	O
license	O
condition	O
,	O
with	O
the	O
last	O
two	O
being	O
intended	O
for	O
other	O
types	O
of	O
works	O
,	O
such	O
as	O
documents	O
and	O
pictures	O
,	O
both	O
academic	O
or	O
artistic	O
in	O
nature	O
.	O
</s>
<s>
An	O
early	O
use	O
of	O
the	O
word	O
copyleft	B-License
was	O
in	O
Li-Chen	O
Wang	O
's	O
Palo	O
Alto	O
Tiny	B-Language
BASIC	I-Language
's	O
distribution	O
notice	O
"	O
@COPYLEFT	B-License
ALL	I-License
WRONGS	I-License
RESERVED	I-License
"	O
in	O
June	O
1976	O
.	O
</s>
<s>
Tiny	B-Language
BASIC	I-Language
was	O
not	O
distributed	O
under	O
any	O
formal	O
form	O
of	O
copyleft	B-License
distribution	O
terms	O
,	O
but	O
it	O
was	O
presented	O
in	O
a	O
context	O
where	O
source	O
code	O
was	O
being	O
shared	O
and	O
modified	O
.	O
</s>
<s>
In	O
fact	O
,	O
Wang	O
had	O
earlier	O
contributed	O
edits	O
to	O
Tiny	B-Language
BASIC	I-Language
Extended	O
before	O
writing	O
his	O
own	O
BASIC	B-Language
interpreter	I-Language
.	O
</s>
<s>
The	O
concept	O
of	O
copyleft	B-License
was	O
described	O
in	O
Richard	O
Stallman	O
's	O
GNU	B-Application
Manifesto	I-Application
in	O
1985	O
,	O
where	O
he	O
wrote	O
:	O
</s>
<s>
Stallman	O
worked	O
a	O
few	O
years	O
earlier	O
on	O
a	O
Lisp	B-Language
interpreter	O
.	O
</s>
<s>
Symbolics	O
asked	O
to	O
use	O
the	O
Lisp	B-Language
interpreter	O
,	O
and	O
Stallman	O
agreed	O
to	O
supply	O
them	O
with	O
a	O
public	B-Application
domain	I-Application
version	O
of	O
his	O
work	O
.	O
</s>
<s>
Symbolics	O
extended	O
and	O
improved	O
the	O
Lisp	B-Language
interpreter	O
,	O
but	O
when	O
Stallman	O
wanted	O
access	O
to	O
the	O
improvements	O
that	O
Symbolics	O
had	O
made	O
to	O
his	O
interpreter	O
,	O
Symbolics	O
refused	O
.	O
</s>
<s>
Stallman	O
then	O
,	O
in	O
1984	O
,	O
proceeded	O
to	O
work	O
towards	O
eradicating	O
this	O
emerging	O
behavior	O
and	O
culture	O
of	O
proprietary	B-Application
software	I-Application
,	O
which	O
he	O
named	O
software	B-License
hoarding	I-License
.	O
</s>
<s>
This	O
was	O
not	O
the	O
first	O
time	O
Stallman	O
had	O
dealt	O
with	O
proprietary	B-Application
software	I-Application
,	O
but	O
he	O
deemed	O
this	O
interaction	O
a	O
"	O
turning	O
point	O
"	O
.	O
</s>
<s>
He	O
justified	O
software	B-Application
sharing	O
,	O
protesting	O
that	O
when	O
sharing	O
,	O
the	B-Application
software	I-Application
online	O
can	O
be	O
copied	O
without	O
the	O
loss	O
of	O
the	O
original	O
piece	O
of	O
work	O
.	O
</s>
<s>
The	B-Application
software	I-Application
can	O
be	O
used	O
multiple	O
times	O
without	O
ever	O
being	O
damaged	O
or	O
worn	O
out	O
.	O
</s>
<s>
As	O
Stallman	O
deemed	O
it	O
impractical	O
in	O
the	O
short	O
term	O
to	O
eliminate	O
current	O
copyright	O
law	O
and	O
the	O
wrongs	O
he	O
perceived	O
it	O
to	O
perpetuate	O
,	O
he	O
decided	O
to	O
work	O
within	O
the	O
framework	O
of	O
existing	O
law	O
;	O
in	O
1985	O
,	O
he	O
created	O
his	O
own	O
copyright	O
license	O
,	O
the	O
Emacs	B-License
General	I-License
Public	I-License
License	I-License
,	O
the	O
first	O
copyleft	B-License
license	I-License
.	O
</s>
<s>
This	O
later	O
evolved	O
into	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
,	O
which	O
is	O
now	O
one	O
of	O
the	O
most	O
popular	O
free-software	B-License
licenses	I-License
.	O
</s>
<s>
This	O
original	O
GPL	B-License
did	O
not	O
grant	O
rights	O
to	O
the	O
public	O
at	O
large	O
,	O
only	O
those	O
who	O
had	O
already	O
received	O
the	O
program	O
;	O
but	O
it	O
was	O
the	O
best	O
that	O
could	O
be	O
done	O
under	O
existing	O
law	O
.	O
</s>
<s>
The	O
new	O
license	O
was	O
not	O
at	O
this	O
time	O
given	O
the	O
copyleft	B-License
label	O
.	O
</s>
<s>
Richard	O
Stallman	O
stated	O
that	O
the	O
use	O
of	O
"	O
Copyleft	B-License
"	O
comes	O
from	O
Don	O
Hopkins	O
,	O
who	O
mailed	O
him	O
a	O
letter	O
in	O
1984	O
or	O
1985	O
,	O
on	O
which	O
was	O
written	O
:	O
"	O
Copyleft	B-License
–	O
all	O
rights	O
reversed	O
"	O
,	O
which	O
is	O
a	O
pun	O
on	O
the	O
common	O
copyright	O
disclaimer	O
.	O
</s>
<s>
In	O
France	O
,	O
a	O
series	O
of	O
meetings	O
taking	O
place	O
in	O
2000	O
under	O
the	O
title	O
"	O
Copyleft	B-License
Attitude	O
"	O
gave	O
birth	O
to	O
the	O
Free	B-Application
Art	O
License	O
(	O
FAL	O
)	O
,	O
theoretically	O
valid	O
in	O
any	O
jurisdiction	O
bound	O
by	O
the	O
Berne	O
Convention	O
and	O
recommended	O
by	O
Stallman	O
's	O
own	O
Free	B-Operating_System
Software	I-Operating_System
Foundation	I-Operating_System
.	O
</s>
<s>
Shortly	O
thereafter	O
,	O
a	O
separate	O
,	O
unrelated	O
initiative	O
in	O
the	O
United	O
States	O
yielded	O
the	O
Creative	O
Commons	O
license	O
,	O
available	O
since	O
2001	O
in	O
several	O
different	O
versions	O
(	O
only	O
some	O
of	O
which	O
can	O
be	O
described	O
as	O
copyleft	B-License
)	O
and	O
more	O
specifically	O
tailored	O
to	O
U.S.	O
law	O
.	O
</s>
<s>
While	O
copyright	O
law	O
gives	O
software	B-Application
authors	O
control	O
over	O
copying	O
,	O
distribution	O
and	O
modification	O
of	O
their	O
works	O
,	O
the	O
goal	O
of	O
copyleft	B-License
is	O
to	O
give	O
all	O
users	O
of	O
the	O
work	O
the	O
freedom	O
to	O
carry	O
out	O
all	O
of	O
these	O
activities	O
.	O
</s>
<s>
These	O
freedoms	O
(	O
from	O
the	B-Application
Free	I-Application
Software	I-Application
Definition	I-Application
)	O
include	O
:	O
</s>
<s>
Similar	O
terms	O
are	O
present	O
in	O
the	B-License
Open	I-License
Source	I-License
Definition	I-License
,	O
a	O
separate	O
definition	O
that	O
contains	O
similar	O
freedoms	O
.	O
</s>
<s>
The	O
vast	O
majority	O
of	O
copyleft	B-License
licenses	I-License
satisfy	O
both	O
definitions	O
,	O
that	O
of	O
the	B-Application
Free	I-Application
Software	I-Application
Definition	I-Application
and	O
Open	B-License
Source	I-License
Definition	I-License
.	O
</s>
<s>
By	O
guaranteeing	O
viewers	O
and	O
users	O
of	O
a	O
work	O
the	O
freedom	O
and	O
permission	O
to	O
reproduce	O
,	O
adapt	O
,	O
or	O
distribute	O
it	O
,	O
copyleft	B-License
licenses	I-License
are	O
distinct	O
from	O
other	O
types	O
of	O
copyright	O
licenses	O
that	O
limit	O
such	O
freedoms	O
.	O
</s>
<s>
Instead	O
of	O
allowing	O
a	O
work	O
to	O
fall	O
completely	O
into	O
the	O
public	B-Application
domain	I-Application
,	O
where	O
no	O
ownership	O
of	O
copyright	O
is	O
claimed	O
,	O
copyleft	B-License
allows	O
authors	O
to	O
impose	O
restrictions	O
on	O
the	O
use	O
of	O
their	O
work	O
.	O
</s>
<s>
One	O
of	O
the	O
main	O
restrictions	O
imposed	O
by	O
copyleft	B-License
is	O
that	O
derived	O
works	O
must	O
also	O
be	O
released	O
under	O
a	O
compatible	O
copyleft	B-License
license	I-License
.	O
</s>
<s>
This	O
is	O
due	O
to	O
the	O
underlying	O
principle	O
of	O
copyleft	B-License
:	O
that	O
anyone	O
can	O
benefit	O
freely	O
from	O
the	O
previous	O
work	O
of	O
others	O
,	O
but	O
that	O
any	O
modifications	O
to	O
that	O
work	O
should	O
benefit	O
everyone	O
else	O
as	O
well	O
,	O
and	O
thus	O
must	O
be	O
released	O
under	O
similar	O
terms	O
.	O
</s>
<s>
For	O
this	O
reason	O
,	O
copyleft	B-License
licenses	I-License
are	O
also	O
known	O
as	O
reciprocal	B-License
licenses	I-License
:	O
any	O
modifiers	O
of	O
a	O
copyleft-licensed	O
work	O
are	O
expected	O
to	O
reciprocate	O
the	O
author	O
's	O
action	O
of	O
copyleft-licensing	O
the	B-Application
software	I-Application
by	O
also	O
copyleft-licensing	O
any	O
derivatives	O
they	O
might	O
have	O
made	O
.	O
</s>
<s>
Because	O
of	O
this	O
requirement	O
,	O
copyleft	B-License
licenses	I-License
have	O
also	O
been	O
described	O
as	O
"	O
viral	O
"	O
due	O
to	O
their	O
self-perpetuating	O
terms	O
.	O
</s>
<s>
In	O
addition	O
to	O
restrictions	O
on	O
copying	O
,	O
copyleft	B-License
licenses	I-License
address	O
other	O
possible	O
impediments	O
.	O
</s>
<s>
In	O
software	B-Application
,	O
this	O
means	O
requiring	O
that	O
the	O
source	O
code	O
of	O
the	O
derived	O
work	O
be	O
made	O
available	O
together	O
with	O
the	B-Application
software	I-Application
itself	O
.	O
</s>
<s>
The	O
economic	O
incentives	O
to	O
work	O
on	O
copyleft	B-License
content	O
can	O
vary	O
.	O
</s>
<s>
When	O
choosing	O
to	O
copyleft	B-License
their	O
work	O
,	O
content	O
creators	O
may	O
seek	O
complementary	O
benefits	O
like	O
recognition	O
from	O
their	O
peers	O
.	O
</s>
<s>
In	O
the	O
world	O
of	O
computer	O
programming	O
,	O
copyleft-licensed	O
computer	O
programs	O
are	O
often	O
created	O
by	O
programmers	O
to	O
fill	O
a	O
need	O
they	O
have	O
noticed	O
.	O
</s>
<s>
Such	O
programs	O
are	O
often	O
published	O
with	O
a	O
copyleft	B-License
license	I-License
simply	O
to	O
ensure	O
that	O
subsequent	O
users	O
can	O
also	O
freely	O
use	O
modified	O
versions	O
of	O
that	O
program	O
.	O
</s>
<s>
This	O
is	O
especially	O
true	O
for	O
creators	O
who	O
wish	O
to	O
prevent	O
"	O
open	B-License
source	I-License
hijacking	O
"	O
,	O
or	O
the	O
act	O
of	O
reusing	O
open-source	B-License
code	O
and	O
then	O
adding	O
extra	O
restrictions	O
to	O
it	O
,	O
an	O
action	O
prevented	O
by	O
copyleft-licensing	O
the	B-Application
software	I-Application
.	O
</s>
<s>
Some	O
creators	O
,	O
such	O
as	O
Elastic	O
,	O
feel	O
that	O
preventing	O
commercial	O
enterprises	O
from	O
using	O
and	O
then	O
selling	O
their	O
product	O
under	O
a	O
proprietary	B-Application
license	I-Application
is	O
also	O
an	O
incentive	O
.	O
</s>
<s>
Furthermore	O
,	O
the	O
open-source	B-License
culture	O
of	O
programming	O
has	O
been	O
described	O
as	O
a	O
gift	O
culture	O
,	O
where	O
social	O
power	O
is	O
determined	O
by	O
an	O
individual	O
's	O
contributions	O
.	O
</s>
<s>
Contributing	O
to	O
or	O
creating	O
open-source	B-License
,	O
copyleft-licensed	O
software	B-Application
of	O
high	O
quality	O
can	O
lead	O
to	O
contributors	O
gaining	O
valuable	O
experience	O
and	O
can	O
lead	O
to	O
future	O
career	O
opportunities	O
.	O
</s>
<s>
Copyleft	B-License
software	B-Application
has	O
economic	O
effects	O
beyond	O
individual	O
creators	O
.	O
</s>
<s>
The	O
presence	O
of	O
quality	O
copyleft	B-License
software	B-Application
can	O
force	O
proprietary	B-Application
software	I-Application
developers	O
to	O
increase	O
the	O
quality	O
of	O
their	O
software	B-Application
to	O
compete	O
with	O
free	B-Application
software	I-Application
.	O
</s>
<s>
This	O
may	O
also	O
have	O
the	O
effect	O
of	O
preventing	O
monopolies	O
in	O
areas	O
dominated	O
by	O
proprietary	B-Application
software	I-Application
.	O
</s>
<s>
However	O
,	O
competition	O
with	O
proprietary	B-Application
software	I-Application
can	O
also	O
be	O
a	O
reason	O
to	O
forgo	O
copyleft	B-License
.	O
</s>
<s>
The	B-Operating_System
Free	I-Operating_System
Software	I-Operating_System
Foundation	I-Operating_System
recommends	O
that	O
when	O
"	O
widespread	O
use	O
of	O
the	O
code	O
is	O
vital	O
for	O
advancing	O
the	O
cause	O
of	O
free	B-Application
software	I-Application
"	O
,	O
allowing	O
the	O
code	O
to	O
be	O
copied	O
and	O
used	O
freely	O
is	O
more	O
important	O
than	O
a	O
copyleft	B-License
.	O
</s>
<s>
Common	O
practice	O
for	O
using	O
copyleft	B-License
is	O
to	O
codify	O
the	O
copying	O
terms	O
for	O
a	O
work	O
with	O
a	O
license	O
.	O
</s>
<s>
Any	O
such	O
license	O
typically	O
includes	O
all	O
the	O
provisions	O
and	O
principles	O
of	O
copyleft	B-License
inside	O
the	O
license	O
's	O
terms	O
.	O
</s>
<s>
Unlike	O
similar	O
permissive	B-License
licenses	I-License
that	O
also	O
grant	O
these	O
freedoms	O
,	O
copyleft	B-License
licenses	I-License
also	O
ensure	O
that	O
any	O
modified	O
versions	O
of	O
a	O
work	O
covered	O
by	O
a	O
copyleft	B-License
license	I-License
must	O
also	O
grant	O
these	O
freedoms	O
.	O
</s>
<s>
Thus	O
,	O
copyleft	B-License
licenses	I-License
have	O
conditions	O
:	O
that	O
modifications	O
of	O
any	O
work	O
licensed	O
under	O
a	O
copyleft	B-License
license	I-License
must	O
be	O
distributed	O
under	O
a	O
compatible	O
copyleft	B-License
scheme	O
and	O
that	O
the	O
distributed	O
modified	O
work	O
must	O
include	O
a	O
means	O
of	O
modifying	O
the	O
work	O
.	O
</s>
<s>
Under	O
fair	O
use	O
,	O
however	O
,	O
copyleft	B-License
licenses	I-License
may	O
be	O
superseded	O
,	O
just	O
like	O
regular	O
copyrights	O
.	O
</s>
<s>
Therefore	O
,	O
any	O
person	O
utilizing	O
a	O
source	O
licensed	O
under	O
a	O
copyleft	B-License
license	I-License
for	O
works	O
they	O
invent	O
is	O
free	B-Application
to	O
choose	O
any	O
other	O
license	O
(	O
or	O
none	O
at	O
all	O
)	O
provided	O
they	O
meet	O
the	O
fair	O
use	O
standard	O
.	O
</s>
<s>
Copyleft	B-License
licenses	I-License
necessarily	O
make	O
creative	O
use	O
of	O
relevant	O
rules	O
and	O
laws	O
to	O
enforce	O
their	O
provisions	O
.	O
</s>
<s>
For	O
example	O
,	O
when	O
using	O
copyright	O
law	O
,	O
those	O
who	O
contribute	O
to	O
a	O
work	O
under	O
copyleft	B-License
usually	O
must	O
gain	O
,	O
defer	O
,	O
or	O
assign	O
copyright	O
holder	O
status	O
.	O
</s>
<s>
By	O
submitting	O
the	O
copyright	O
of	O
their	O
contributions	O
under	O
a	O
copyleft	B-License
license	I-License
,	O
they	O
deliberately	O
give	O
up	O
some	O
of	O
the	O
rights	O
that	O
normally	O
follow	O
from	O
copyright	O
,	O
including	O
the	O
right	O
to	O
be	O
the	O
unique	O
distributor	O
of	O
copies	O
of	O
the	O
work	O
.	O
</s>
<s>
Some	O
laws	O
used	O
for	O
copyleft	B-License
licenses	I-License
vary	O
from	O
one	O
country	O
to	O
another	O
,	O
and	O
may	O
also	O
be	O
granted	O
in	O
terms	O
that	O
vary	O
from	O
country	O
to	O
country	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
some	O
countries	O
,	O
it	O
is	O
acceptable	O
to	O
sell	O
a	O
software	B-Application
product	I-Application
without	O
warranty	O
,	O
in	O
standard	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
style	O
,	O
while	O
in	O
most	O
European	O
countries	O
it	O
is	O
not	O
permitted	O
for	O
a	O
software	B-Application
distributor	O
to	O
waive	O
all	O
warranties	O
regarding	O
a	O
sold	O
product	O
.	O
</s>
<s>
For	O
this	O
reason	O
,	O
the	O
extent	O
of	O
such	O
warranties	O
is	O
specified	O
in	O
most	O
European	O
copyleft	B-License
licenses	I-License
,	O
for	O
example	O
,	O
the	O
European	O
Union	O
Public	O
Licence	O
(	O
EUPL	O
)	O
,	O
or	O
the	O
CeCILL	B-License
license	I-License
,	O
a	O
license	O
that	O
allows	O
one	O
to	O
use	O
GNU	B-License
GPL	I-License
in	O
combination	O
with	O
a	O
limited	O
warranty	O
.	O
</s>
<s>
For	O
projects	O
which	O
will	O
be	O
run	O
over	O
a	O
network	O
,	O
a	O
variation	O
of	O
the	O
GNU	B-License
GPL	I-License
,	O
called	O
the	O
Affero	O
General	B-License
Public	I-License
License	I-License
(	O
GNU	B-Application
AGPL	I-Application
)	O
,	O
ensures	O
that	O
the	O
source	O
code	O
is	O
available	O
to	O
users	O
of	O
software	B-Application
over	O
a	O
network	O
.	O
</s>
<s>
Free	B-Application
Non-freePublic	O
domain	O
&	O
equivalents	O
Copyleft	B-License
(	O
protective	O
license	O
)	O
Proprietary	B-Application
license	I-Application
Trade	O
secret	O
Description	O
Grants	O
all	O
rights	O
Grants	O
use	O
rights	O
,	O
including	O
right	O
to	O
relicense	O
(	O
allows	O
proprietization	B-Application
,	O
license	O
compatibility	O
)	O
Grants	O
use	O
rights	O
,	O
forbids	O
proprietization	B-Application
Grants	O
rights	O
for	O
noncommercial	O
use	O
only	O
.	O
</s>
<s>
Copyleft	B-License
is	O
a	O
distinguishing	O
feature	O
of	O
some	O
free	B-License
software	I-License
licenses	I-License
,	O
while	O
other	O
free-software	B-License
licenses	I-License
are	O
not	O
copyleft	B-License
licenses	I-License
because	O
they	O
do	O
not	O
require	O
the	O
licensee	O
to	O
distribute	O
derivative	O
works	O
under	O
the	O
same	O
license	O
.	O
</s>
<s>
This	O
debate	O
hinges	O
on	O
complex	O
issues	O
,	O
such	O
as	O
the	O
definition	O
of	O
freedom	O
and	O
whose	O
freedoms	O
are	O
more	O
important	O
:	O
the	O
potential	O
future	O
recipients	O
of	O
a	O
work	O
(	O
freedom	O
from	O
proprietization	B-Application
)	O
or	O
just	O
the	O
initial	O
recipient	O
(	O
freedom	O
to	O
proprietize	B-Application
)	O
.	O
</s>
<s>
However	O
,	O
current	O
copyright	O
law	O
and	O
the	O
availability	O
of	O
both	O
types	O
of	O
licenses	O
,	O
copyleft	B-License
and	O
permissive	B-License
,	O
allow	O
authors	O
to	O
choose	O
the	O
type	O
under	O
which	O
to	O
license	O
the	O
works	O
they	O
invent	O
.	O
</s>
<s>
For	O
documents	O
,	O
art	O
,	O
and	O
other	O
works	O
other	O
than	O
software	B-Application
and	O
code	O
,	O
the	O
Creative	O
Commons	O
share-alike	O
licensing	O
system	O
and	O
the	O
GNU	B-Application
Free	I-Application
Documentation	I-Application
License	I-Application
(	O
GFDL	B-Application
)	O
allow	O
authors	O
to	O
apply	O
limitations	O
to	O
certain	O
sections	O
of	O
their	O
work	O
,	O
exempting	O
some	O
parts	O
of	O
the	O
work	O
from	O
the	O
full	B-License
copyleft	I-License
mechanism	O
.	O
</s>
<s>
In	O
the	O
case	O
of	O
the	O
GFDL	B-Application
,	O
these	O
limitations	O
include	O
the	O
use	O
of	O
invariant	O
sections	O
,	O
which	O
may	O
not	O
be	O
altered	O
by	O
future	O
editors	O
.	O
</s>
<s>
The	O
initial	O
intention	O
of	O
the	O
GFDL	B-Application
was	O
as	O
a	O
device	O
for	O
supporting	O
the	O
documentation	O
of	O
copylefted	B-License
software	B-Application
.	I-Application
</s>
<s>
The	O
strength	O
of	O
the	O
copyleft	B-License
license	I-License
governing	O
a	O
work	O
is	O
determined	O
by	O
the	O
extent	O
to	O
its	O
provisions	O
can	O
be	O
imposed	O
on	O
all	O
kinds	O
of	O
derivative	O
works	O
.	O
</s>
<s>
Thus	O
,	O
the	O
term	O
"	O
weak	O
copyleft	B-License
"	O
refers	O
to	O
licenses	O
where	O
not	O
all	O
derivative	O
works	O
inherit	O
the	O
copyleft	B-License
license	I-License
;	O
whether	O
a	O
derivative	O
work	O
inherits	O
or	O
not	O
often	O
depends	O
on	O
how	O
it	O
was	O
derived	O
.	O
</s>
<s>
"	O
Weak	O
copyleft	B-License
"	O
licenses	O
are	O
often	O
used	O
to	O
cover	O
software	B-Library
libraries	I-Library
.	O
</s>
<s>
This	O
allows	O
other	O
software	B-Application
to	O
link	O
to	O
the	O
library	O
and	O
be	O
redistributed	O
without	O
the	O
requirement	O
for	O
the	O
linking	O
software	B-Application
to	O
also	O
be	O
licensed	O
under	O
the	O
same	O
terms	O
.	O
</s>
<s>
Only	O
changes	O
to	O
the	B-Application
software	I-Application
licensed	O
under	O
a	O
"	O
weak	O
copyleft	B-License
"	O
license	O
become	O
subject	O
itself	O
to	O
copyleft	B-License
provisions	O
of	O
such	O
a	O
license	O
.	O
</s>
<s>
This	O
allows	O
programs	O
of	O
any	O
license	O
to	O
be	O
compiled	O
and	O
linked	O
against	O
copylefted	B-License
libraries	O
such	O
as	O
glibc	B-Language
and	O
then	O
redistributed	O
without	O
any	O
re-licensing	O
required	O
.	O
</s>
<s>
The	O
concrete	O
effect	O
of	O
strong	O
vs.	O
weak	O
copyleft	B-License
has	O
yet	O
to	O
be	O
tested	O
in	O
court	O
.	O
</s>
<s>
Free-software	B-License
licenses	I-License
that	O
use	O
"	O
weak	O
"	O
copyleft	B-License
include	O
the	O
GNU	B-Application
Lesser	I-Application
General	I-Application
Public	I-Application
License	I-Application
and	O
the	O
Mozilla	B-License
Public	I-License
License	I-License
.	O
</s>
<s>
The	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
is	O
an	O
example	O
of	O
a	O
license	O
implementing	O
strong	O
copyleft	B-License
.	O
</s>
<s>
A	O
stronger	O
copyleft	B-License
license	I-License
is	O
the	O
AGPL	B-Application
,	O
which	O
requires	O
the	O
publishing	O
of	O
the	O
source	O
code	O
for	O
software	B-Architecture
as	I-Architecture
a	I-Architecture
service	I-Architecture
use	O
cases	O
.	O
</s>
<s>
The	O
Sybase	O
Open	O
Watcom	O
Public	O
License	O
is	O
one	O
of	O
the	O
strongest	O
copyleft	B-License
licenses	I-License
,	O
as	O
this	O
license	O
closes	O
the	O
so-called	O
"	O
private	O
usage	O
"	O
loophole	O
of	O
the	O
GPL	B-License
,	O
and	O
requires	O
the	O
publishing	O
of	O
source	O
code	O
in	O
any	O
use	O
case	O
.	O
</s>
<s>
For	O
this	O
reason	O
,	O
the	O
license	O
is	O
considered	O
non-free	B-Application
by	O
the	B-Operating_System
Free	I-Operating_System
Software	I-Operating_System
Foundation	I-Operating_System
,	O
the	B-Application
GNU	I-Application
Project	I-Application
,	O
and	O
the	O
Debian	O
project	O
.	O
</s>
<s>
However	O
,	O
the	O
license	O
is	O
accepted	O
as	O
open	B-License
source	I-License
by	O
the	O
OSI	O
.	O
</s>
<s>
The	O
Design	O
Science	O
License	O
(	O
DSL	O
)	O
is	O
a	O
strong	O
copyleft	B-License
license	I-License
that	O
applies	O
to	O
any	O
work	O
,	O
not	O
only	O
software	B-Application
or	O
documentation	O
,	O
but	O
also	O
literature	O
,	O
artworks	O
,	O
music	O
,	O
photography	O
,	O
and	O
video	O
.	O
</s>
<s>
DSL	O
was	O
written	O
by	O
Michael	O
Stutz	O
after	O
he	O
took	O
an	O
interest	O
in	O
applying	O
GNU-style	O
copyleft	B-License
to	O
non-software	O
works	O
,	O
which	O
later	O
came	O
to	O
be	O
called	O
libre	O
works	O
.	O
</s>
<s>
It	O
is	O
not	O
considered	O
compatible	O
with	O
the	O
GNU	B-License
GPL	I-License
by	O
the	B-Operating_System
Free	I-Operating_System
Software	I-Operating_System
Foundation	I-Operating_System
.	O
</s>
<s>
"	O
Full	O
"	O
and	O
"	O
partial	O
"	O
copyleft	B-License
relate	O
to	O
another	O
issue	O
.	O
</s>
<s>
Full	B-License
copyleft	I-License
exists	O
when	O
all	O
parts	O
of	O
a	O
work	O
(	O
except	O
the	O
license	O
itself	O
)	O
may	O
only	O
be	O
modified	O
and	O
distributed	O
under	O
the	O
terms	O
of	O
the	O
work	O
's	O
copyleft	B-License
license	I-License
.	O
</s>
<s>
Partial	B-License
copyleft	I-License
,	O
by	O
contrast	O
,	O
exempts	O
some	O
parts	O
of	O
the	O
work	O
from	O
the	O
copyleft	B-License
provisions	O
,	O
permitting	O
distribution	O
of	O
some	O
modifications	O
under	O
terms	O
other	O
than	O
the	O
copyleft	B-License
license	I-License
,	O
or	O
in	O
some	O
other	O
way	O
does	O
not	O
impose	O
all	O
the	O
principles	O
of	O
copylefting	O
on	O
the	O
work	O
.	O
</s>
<s>
An	O
example	O
of	O
partial	B-License
copyleft	I-License
is	O
the	O
GPL	B-Application
linking	I-Application
exception	I-Application
made	O
for	O
some	O
software	B-Application
packages	O
.	O
</s>
<s>
This	O
implies	O
that	O
any	O
copyleft	B-License
license	I-License
is	O
automatically	O
a	O
share-alike	O
license	O
but	O
not	O
the	O
other	O
way	O
around	O
,	O
as	O
some	O
share-alike	O
licenses	O
include	O
further	O
restrictions	O
such	O
as	O
prohibiting	O
commercial	O
use	O
.	O
</s>
<s>
Some	O
Creative	O
Commons	O
licenses	O
are	O
examples	O
of	O
share-alike	O
copyleft	B-License
licenses	I-License
.	O
</s>
<s>
Those	O
licenses	O
grant	O
users	O
of	O
the	B-Application
software	I-Application
the	O
same	O
freedoms	O
as	O
copyleft	B-License
licenses	I-License
but	O
do	O
not	O
require	O
modified	O
versions	O
of	O
that	O
software	B-Application
to	O
also	O
include	O
those	O
freedoms	O
.	O
</s>
<s>
They	O
have	O
minimal	O
restrictions	O
on	O
how	O
the	B-Application
software	I-Application
can	O
be	O
used	O
,	O
modified	O
,	O
and	O
redistributed	O
,	O
and	O
are	O
thus	O
not	O
copyleft	B-License
licenses	I-License
.	O
</s>
<s>
Examples	O
of	O
this	O
type	O
of	O
license	O
include	O
the	O
X11	B-License
license	I-License
,	O
Apache	B-Application
license	I-Application
,	O
Expat	B-License
license	I-License
,	O
and	O
the	O
various	O
BSD	B-Operating_System
licenses	I-Operating_System
.	O
</s>
<s>
It	O
has	O
been	O
suggested	O
that	O
copyleft	B-License
has	O
become	O
a	O
divisive	O
issue	O
in	O
the	O
ideological	O
strife	O
between	O
the	O
Open	B-License
Source	I-License
Initiative	O
and	O
the	O
free	B-Application
software	I-Application
movement	O
.	O
</s>
<s>
However	O
,	O
there	O
is	O
evidence	O
that	O
copyleft	B-License
is	O
both	O
accepted	O
and	O
proposed	O
by	O
both	O
parties	O
:	O
</s>
<s>
Both	O
the	O
OSI	O
and	O
the	O
FSF	B-Operating_System
have	O
copyleft	B-License
and	O
non-copyleft	B-License
licenses	O
in	O
their	O
respective	O
lists	O
of	O
accepted	O
licenses	O
.	O
</s>
<s>
The	O
OSI	O
's	O
original	O
Legal	O
Counsel	O
Lawrence	O
Rosen	O
has	O
written	O
a	O
copyleft	B-License
license	I-License
,	O
the	O
Open	B-License
Software	I-License
License	I-License
.	O
</s>
<s>
The	O
OSI	O
's	O
licensing	O
how-to	O
recognises	O
the	O
GPL	B-License
as	O
a	O
"	O
best	O
practice	O
"	O
license	O
.	O
</s>
<s>
Some	O
of	O
the	B-Application
software	I-Application
programs	O
of	O
the	B-Application
GNU	I-Application
Project	I-Application
are	O
published	O
under	O
non-copyleft	B-License
licenses	O
.	O
</s>
<s>
Stallman	O
himself	O
has	O
endorsed	O
the	O
use	O
of	O
non-copyleft	B-License
licenses	O
in	O
certain	O
circumstances	O
,	O
most	O
recently	O
in	O
the	O
case	O
of	O
the	O
Ogg	B-Algorithm
Vorbis	I-Algorithm
license	O
change	O
.	O
</s>
<s>
Viral	O
license	O
is	O
a	O
pejorative	O
name	O
for	O
copyleft	B-License
licenses	I-License
.	O
</s>
<s>
It	O
originates	O
from	O
the	O
terms	O
'	O
General	B-License
Public	I-License
Virus	I-License
 '	O
or	O
'	O
GNU	B-License
Public	I-License
Virus	I-License
 '	O
(	O
GPV	O
)	O
,	O
which	O
dates	O
back	O
to	O
1990	O
,	O
a	O
year	O
after	O
the	O
GPLv1	O
was	O
released	O
.	O
</s>
<s>
The	O
name	O
"	O
viral	O
licenses	O
"	O
refers	O
to	O
the	O
fact	O
that	O
any	O
works	O
derived	O
from	O
a	O
copyleft	B-License
work	O
must	O
preserve	O
the	O
copyleft	B-License
permissions	I-License
when	O
distributed	O
.	O
</s>
<s>
Some	O
advocates	O
of	O
the	O
various	O
BSD	B-Operating_System
Licenses	I-Operating_System
used	O
the	O
term	O
derisively	O
in	O
regards	O
to	O
the	O
GPL	B-License
's	O
tendency	O
to	O
absorb	O
BSD-licensed	O
code	O
without	O
allowing	O
the	O
original	O
BSD	B-Operating_System
work	O
to	O
benefit	O
from	O
it	O
,	O
while	O
at	O
the	O
same	O
time	O
promoting	O
itself	O
as	O
"	O
freer	O
"	O
than	O
other	O
licenses	O
.	O
</s>
<s>
Microsoft	O
vice-president	O
Craig	O
Mundie	O
remarked	O
,	O
"	O
This	O
viral	O
aspect	O
of	O
the	O
GPL	B-License
poses	O
a	O
threat	O
to	O
the	O
intellectual	O
property	O
of	O
any	O
organization	O
making	O
use	O
of	O
it.	O
"	O
</s>
<s>
In	O
another	O
context	O
,	O
Steve	O
Ballmer	O
declared	O
that	O
code	O
released	O
under	O
GPL	B-License
is	O
useless	O
to	O
the	O
commercial	O
sector	O
,	O
since	O
it	O
can	O
only	O
be	O
used	O
if	O
the	O
resulting	O
surrounding	O
code	O
is	O
licensed	O
under	O
a	O
GPL-compatible	O
license	O
,	O
and	O
described	O
it	O
thus	O
as	O
"	O
a	O
cancer	O
that	O
attaches	O
itself	O
in	O
an	O
intellectual	O
property	O
sense	O
to	O
everything	O
it	O
touches	O
"	O
.	O
</s>
<s>
In	O
response	O
to	O
Microsoft	O
's	O
attacks	O
on	O
the	O
GPL	B-License
,	O
several	O
prominent	O
free-software	B-Application
developers	O
and	O
advocates	O
released	O
a	O
joint	O
statement	O
supporting	O
the	O
license	O
.	O
</s>
<s>
According	O
to	O
FSF	B-Operating_System
compliance	O
engineer	O
David	O
Turner	O
,	O
the	O
term	O
"	O
viral	O
license	O
"	O
creates	O
a	O
misunderstanding	O
and	O
a	O
fear	O
of	O
using	O
copylefted	B-License
free	B-Application
software	I-Application
.	O
</s>
<s>
David	O
McGowan	O
has	O
also	O
written	O
that	O
there	O
is	O
no	O
reason	O
to	O
believe	O
the	O
GPL	B-License
could	O
force	O
proprietary	B-Application
software	I-Application
to	O
become	O
free	B-Application
software	I-Application
,	O
but	O
could	O
"	O
try	O
to	O
enjoin	O
the	O
firm	O
from	O
distributing	O
commercially	O
a	O
program	O
that	O
combined	O
with	O
the	O
GPL	B-License
'd	O
code	O
to	O
form	O
a	O
derivative	O
work	O
,	O
and	O
to	O
recover	O
damages	O
for	O
infringement.	O
"	O
</s>
<s>
If	O
the	O
firm	O
"	O
actually	O
copied	O
code	O
from	O
a	O
GPL	B-License
'd	O
program	O
,	O
such	O
a	O
suit	O
would	O
be	O
a	O
perfectly	O
ordinary	O
assertion	O
of	O
copyright	O
,	O
which	O
most	O
private	O
firms	O
would	O
defend	O
if	O
the	O
shoe	O
were	O
on	O
the	O
other	O
foot.	O
"	O
</s>
<s>
Richard	O
Stallman	O
has	O
described	O
this	O
view	O
with	O
an	O
analogy	O
,	O
saying	O
,	O
"	O
The	O
GPL	B-License
's	O
domain	O
does	O
not	O
spread	O
by	O
proximity	O
or	O
contact	O
,	O
only	O
by	O
deliberate	O
inclusion	O
of	O
GPL-covered	O
code	O
in	O
your	O
program	O
.	O
</s>
<s>
Popular	O
copyleft	B-License
licenses	I-License
,	O
such	O
as	O
the	O
GPL	B-License
,	O
have	O
a	O
clause	O
allowing	O
components	O
to	O
interact	O
with	O
non-copyleft	B-License
components	O
as	O
long	O
as	O
the	O
communication	O
is	O
abstract	O
,	O
such	O
as	O
executing	O
a	O
command-line	O
tool	O
with	O
a	O
set	O
of	O
switches	O
or	O
interacting	O
with	O
a	O
web	O
server	O
.	O
</s>
<s>
As	O
a	O
consequence	O
,	O
even	O
if	O
one	O
module	O
of	O
an	O
otherwise	O
non-copyleft	B-License
product	O
is	O
placed	O
under	O
the	O
GPL	B-License
,	O
it	O
may	O
still	O
be	O
legal	O
for	O
other	O
components	O
to	O
communicate	O
with	O
it	O
in	O
ways	O
such	O
as	O
these	O
.	O
</s>
<s>
This	O
allowed	O
communication	O
may	O
or	O
may	O
not	O
include	O
reusing	O
libraries	O
or	O
routines	O
via	O
dynamic	B-Library
linking	I-Library
–	O
some	O
commentators	O
say	O
it	O
does	O
,	O
the	O
FSF	B-Operating_System
asserts	O
it	O
does	O
not	O
and	O
explicitly	O
adds	O
an	O
exception	B-Application
allowing	I-Application
it	I-Application
in	O
the	O
license	O
for	O
the	O
GNU	B-Language
Classpath	I-Language
re-implementation	O
of	O
the	O
Java	O
library	O
.	O
</s>
<s>
This	O
ambiguity	O
is	O
an	O
important	O
difference	O
between	O
the	O
GPL	B-License
and	O
the	O
LGPL	B-Application
,	O
in	O
that	O
the	O
LGPL	B-Application
specifically	O
allows	O
linking	O
or	O
compiling	O
works	O
licensed	O
under	O
terms	O
that	O
are	O
not	O
compatible	O
with	O
the	O
LGPL	B-Application
,	O
with	O
works	O
covered	O
by	O
the	O
LGPL	B-Application
.	O
</s>
<s>
The	O
copyleft	B-License
symbol	I-License
is	O
a	O
rotated	O
version	O
of	O
the	O
copyright	O
symbol	O
,	O
:	O
an	O
,	O
inverted	O
,	O
reversed	O
in	O
a	O
circle	O
.	O
</s>
