mathlib

d94370d1 - feat(analysis/special_functions/trigonometric/basic): `tan_pi_div_two_sub` (#17024)

feat(analysis/special_functions/trigonometric/basic): `tan_pi_div_two_sub` (#17024) We have lemmas `sin_pi_div_two_sub` and `cos_pi_div_two_sub`. Add corresponding `tan_pi_div_two_sub` lemmas (real and complex).