Logic: Output a 1 when a = 1 and b = 0
I'm pretty sure half a 7402 is all you need: use one gate to invert A and the other to NOR it with B:







simulate this circuit &ndash; Schematic created using CircuitLab

 A   A'  B  |  Y
------------+----
 0   1   0  |  0
 0   1   1  |  0
 1   0   0  |  1
 1   0   1  |  0