no goals
x y : ℝ
h :
  ((∀ (k : ℤ), x ≠ (2 * ↑k + 1) * π / 2) ∧ ∀ (l : ℤ), y ≠ (2 * ↑l + 1) * π / 2) ∨
    (∃ k, x = (2 * ↑k + 1) * π / 2) ∧ ∃ l, y = (2 * ↑l + 1) * π / 2
⊢ tan (x + y) = (tan x + tan y) / (1 - tan x * tan y)
simpa only [← Complex.ofReal_inj, Complex.ofReal_sub, Complex.ofReal_add, Complex.ofReal_div,
  Complex.ofReal_mul, Complex.ofReal_tan] using
  @Complex.tan_add (x : ℂ) (y : ℂ) (by convert h <;> norm_cast)
no goals
x y : ℝ
h :
  ((∀ (k : ℤ), x ≠ (2 * ↑k + 1) * π / 2) ∧ ∀ (l : ℤ), y ≠ (2 * ↑l + 1) * π / 2) ∨
    (∃ k, x = (2 * ↑k + 1) * π / 2) ∧ ∃ l, y = (2 * ↑l + 1) * π / 2
⊢ ((∀ (k : ℤ), ↑x ≠ (2 * ↑k + 1) * ↑π / 2) ∧ ∀ (l : ℤ), ↑y ≠ (2 * ↑l + 1) * ↑π / 2) ∨
    (∃ k, ↑x = (2 * ↑k + 1) * ↑π / 2) ∧ ∃ l, ↑y = (2 * ↑l + 1) * ↑π / 2
convert h <;> norm_cast