Commit 2021-04-14 23:14 4605b55d

feat(algebra/big_operators/finprod): add a few lemmas (#7130)

• add finprod_nonneg, finprod_cond_nonneg, and finprod_eq_zero;
• use α → Prop instead of set α in finprod_mem_eq_prod_of_mem_iff, rename to finprod_cond_eq_prod_of_cond_iff.