a and not b will negate b.
This is perfectly unclear statement.
Obviously, here "a" will be evaluated, if it is false, no further processing continues and "false" is returned, because FPC, as far as I remember, uses lazy evaluation.
If "a" is true, it evaluates "not b"; if "not b" is false, it stops with "false" as result, otherwise "and" is evaluated and "true" returned.
Obviously, this is much more than just negation of b.
So, what did you want to say apart from being arrogant, as usually, is not clear.