Ah, yes... very good. And I guess that could be written this way as
well...

=NOT(A1)+NOT(B1)=1
...

If A1 and B1 would always be 1s or 0s, even shorter:

=MOD(A1+B1,2)

Provided the user didn't need to see the result of the operation as
TRUE/FALSE, of course.

--
Rick (MVP - Excel)