`_mexpand` is already defined in simplify and sqrtdenest as meaning multinomial and mul expansion. I see here, now, that you are doing the `power_exp`, too. Could you just rename it to be `_pemexpand` so it's clear that this is different...also, have you checked to make sure that the order of multinomial and `power_exp` doesn't matter? As I recall, the ordering of hints matters in some cases so you might want to make that explicit. You will note in the other definitiions of `_mexpand` that the order is fixed.