I'm having trouble setting a pattern for simplifying a complex expression. I've distilled the question down to the simplest case where Mathematica seems to fail.
I set up a simple rule based on a pattern:
simpRule = a b v___ - c d v___ -> e v
which works on the direct case
a b - c d /. simpRule e
but fails if I simply add a minus sign.
-a b + c d /. simpRule -a b + c d
How do I go about writing a more robust rule? Or perhaps there's a better way to go about performing simplifications of this sort?