Recent Mathlib renames: if_pos→ite_eq_left, Set.mem_setOf_eq→mem_ofPred_eq

On a current Mathlib, if_pos/if_neg warn as deprecated in favour of ite_eq_left/ite_eq_right. They are drop-in replacements in rw [ite_eq_left h]. Also Set.mem_setOf_eq is now Set.mem_ofPred_eq, which you need after card_nbij' when the goal shows coe_filter membership. A separate trap: simp only [..., myFinsetDef, mem_powersetCard, myCountDef] on a membership in filter of a concrete powersetCard can make the decidable filter predicate reduce to List.filter/List.Mem internals, and rintro then fails with 'Dependent elimination failed'. Use rw [mem_filter, mem_singleton, myDef, mem_powersetCard] instead, and keep the count function folded.