<s>
In	O
linguistics	O
,	O
Heaps	B-General_Concept
 '	I-General_Concept
law	I-General_Concept
(	O
also	O
called	O
Herdan	B-General_Concept
's	I-General_Concept
law	I-General_Concept
)	O
is	O
an	O
empirical	O
law	O
which	O
describes	O
the	O
number	O
of	O
distinct	O
words	O
in	O
a	O
document	O
(	O
or	O
set	O
of	O
documents	O
)	O
as	O
a	O
function	O
of	O
the	O
document	O
length	O
(	O
so	O
called	O
type-token	O
relation	O
)	O
.	O
</s>
<s>
Under	O
mild	O
assumptions	O
,	O
the	O
Herdan	O
–	O
Heaps	B-General_Concept
law	I-General_Concept
is	O
asymptotically	O
equivalent	O
to	O
Zipf	O
's	O
law	O
concerning	O
the	O
frequencies	O
of	O
individual	O
words	O
within	O
a	O
text	O
.	O
</s>
<s>
Heaps	B-General_Concept
 '	I-General_Concept
law	I-General_Concept
means	O
that	O
as	O
more	O
instance	O
text	O
is	O
gathered	O
,	O
there	O
will	O
be	O
diminishing	O
returns	O
in	O
terms	O
of	O
discovery	O
of	O
the	O
full	O
vocabulary	O
from	O
which	O
the	O
distinct	O
terms	O
are	O
drawn	O
.	O
</s>
<s>
Heaps	B-General_Concept
 '	I-General_Concept
law	I-General_Concept
also	O
applies	O
to	O
situations	O
in	O
which	O
the	O
"	O
vocabulary	O
"	O
is	O
just	O
some	O
set	O
of	O
distinct	O
types	O
which	O
are	O
attributes	O
of	O
some	O
collection	O
of	O
objects	O
.	O
</s>
<s>
If	O
persons	O
are	O
selected	O
randomly	O
(	O
that	O
is	O
,	O
we	O
are	O
not	O
selecting	O
based	O
on	O
country	O
of	O
origin	O
)	O
,	O
then	O
Heaps	B-General_Concept
 '	I-General_Concept
law	I-General_Concept
says	O
we	O
will	O
quickly	O
have	O
representatives	O
from	O
most	O
countries	O
(	O
in	O
proportion	O
to	O
their	O
population	O
)	O
but	O
it	O
will	O
become	O
increasingly	O
difficult	O
to	O
cover	O
the	O
entire	O
set	O
of	O
countries	O
by	O
continuing	O
this	O
method	O
of	O
sampling	O
.	O
</s>
<s>
Heaps	B-General_Concept
 '	I-General_Concept
law	I-General_Concept
has	O
been	O
observed	O
also	O
in	O
single-cell	O
transcriptomes	O
considering	O
genes	O
as	O
the	O
distinct	O
objects	O
in	O
the	O
"	O
vocabulary	O
"	O
.	O
</s>
