<s>
In	O
computer	B-General_Concept
science	I-General_Concept
,	O
a	O
bidirectional	B-Data_Structure
map	I-Data_Structure
is	O
an	O
associative	B-Application
data	I-Application
structure	I-Application
in	O
which	O
the	O
pairs	O
form	O
a	O
one-to-one	B-Algorithm
correspondence	I-Algorithm
.	O
</s>
<s>
A	O
pair	O
thus	O
provides	O
a	O
unique	B-Algorithm
coupling	I-Algorithm
between	O
and	O
so	O
that	O
can	O
be	O
found	O
when	O
is	O
used	O
as	O
a	O
key	O
and	O
can	O
be	O
found	O
when	O
is	O
used	O
as	O
a	O
key	O
.	O
</s>
<s>
Mathematically	O
,	O
a	O
bidirectional	B-Data_Structure
map	I-Data_Structure
can	O
be	O
defined	O
a	O
bijection	B-Algorithm
between	O
two	O
different	O
sets	O
of	O
keys	O
and	O
of	O
equal	O
cardinality	B-Application
,	O
thus	O
constituting	O
an	O
injective	O
and	O
surjective	B-Algorithm
function	I-Algorithm
:	O
</s>
