<s>
Access	B-General_Concept
structures	I-General_Concept
are	O
used	O
in	O
the	O
study	O
of	O
security	O
systems	O
where	O
multiple	O
parties	O
need	O
to	O
work	O
together	O
to	O
obtain	O
a	O
resource	O
.	O
</s>
<s>
In	O
set	O
theoretic	O
terms	O
they	O
are	O
referred	O
to	O
as	O
qualified	O
sets	O
;	O
in	O
turn	O
,	O
the	O
set	O
of	O
all	O
such	O
qualified	O
sets	O
is	O
called	O
the	O
access	B-General_Concept
structure	I-General_Concept
of	O
the	O
system	O
.	O
</s>
<s>
Only	O
subgroups	O
of	O
participants	O
contained	O
in	O
the	O
access	B-General_Concept
structure	I-General_Concept
are	O
able	O
to	O
join	O
their	O
shares	O
to	O
recompute	O
the	O
secret	O
.	O
</s>
<s>
It	O
is	O
reasonable	O
to	O
assume	O
that	O
access	B-General_Concept
structures	I-General_Concept
are	O
monotone	O
in	O
the	O
sense	O
that	O
,	O
if	O
a	O
subset	O
S	O
is	O
in	O
the	O
access	B-General_Concept
structure	I-General_Concept
,	O
all	O
sets	O
that	O
contain	O
S	O
as	O
a	O
subset	O
should	O
also	O
form	O
part	O
of	O
the	O
access	B-General_Concept
structure	I-General_Concept
.	O
</s>
