Logic gate used in
reversible computation. Has
3 inputs:
 Inputs A1 and A2 are control lines, and are copied unchanged to outputs A1' and A2'.
 Input B is the data line; it is copied unchanged to output B' if A1=0 or A2=0, otherwise it is inverted on B'.
In conventional terms, A1'=A1, A2'=A2 and B'=B
xor (A1
and A2).
The controlled controlled not gate is universal: you can build computers using just this gate.
A1 o

A2 o

B x
Abbreviation: CCN.