> > A  _____/^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> >
> > B  ^^^^^\________/^^^^^^^\_____________
> >

Lots of ways to do it.....
Fundamentally depends upon whether you are looking for
"when A= high and B= low, output = high"
or
"when A is rising and B is sinking, output = high but when A+B stable,
output = low"
If no.1 then it's simple using NAND gates (4 * 2-input NAND gate in a DIP)
or a INV gate and an AND gate (fewer gates but 2 DIPs needed).
If no.2 then a few solutions are possible
Off the top of my head, how about op-amp in differentiator set-up to assess
signal change.  Voltage comparator on outputs, invert B then AND gate.......
Problem lies with getting the op-amp to work correctly as a differentiator.

Ben

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