mathlib

411b67f5 - feat(analysis/special_functions/trigonometric/arctan): `arctan_eq_arccos`, `arccos_eq_arctan` (#17172)

feat(analysis/special_functions/trigonometric/arctan): `arctan_eq_arccos`, `arccos_eq_arctan` (#17172) Add two lemmas analogous to the existing `arctan_eq_arcsin`, `arcsin_eq_arctan`, `arccos_eq_arcsin`, `arcsin_eq_arccos`.