proposition: Lemma cosBpihalf a : cos (a - pi / 2) = sin a.
proof: Proof. by rewrite cosB cos_pihalf mulr0 add0r sin_pihalf mulr1. Qed.
imports: mathcomp(all_ssreflect ssralg ssrint ssrnum matrix) mathcomp(interval rat) mathcomp(mathcomp_extra boolp classical_sets functions) reals ereal nsatz_realtype signed topology normedtype landau sequences derive realfun exp