mathlib3

b1e56a21 - feat(analysis/special_functions/trigonometric): Added lemma cos_ne_zero_iff (#3743)

feat(analysis/special_functions/trigonometric): Added lemma cos_ne_zero_iff (#3743) I added the theorem `cos_ne_zero_iff`, a corollary to the preexisting theorem `cos_eq_zero_iff` <!-- put comments you want to keep out of the PR commit here -->