no goals
x y : ℂ
h :
  ((∀ (k : ℤ), x ≠ (2 * ↑k + 1) * ↑π / 2) ∧ ∀ (l : ℤ), y * I ≠ (2 * ↑l + 1) * ↑π / 2) ∨
    (∃ k, x = (2 * ↑k + 1) * ↑π / 2) ∧ ∃ l, y * I = (2 * ↑l + 1) * ↑π / 2
⊢ tan (x + y * I) = (tan x + tanh y * I) / (1 - tan x * tanh y * I)
rw [tan_add h, tan_mul_I, mul_assoc]