exact this
ℕ : Type
inst✝⁷ : Natural ℕ
ℤ : Type
inst✝⁶ : Core ℤ
inst✝⁵ : Addition ℤ
inst✝⁴ : Multiplication ℤ
inst✝³ : Negation ℤ
inst✝² : Sign ℤ
a b : ℤ
inst✝¹ : Sqrt1 (sgn a)
inst✝ : Sqrt1 (sgn b)
nws_a : NonzeroWithSign a (sgn a)
nws_b : NonzeroWithSign b (sgn b)
this : NonzeroWithSign (a * b) (sgn a * sgn b)
⊢ NonzeroWithSign (a * b) (sgn a * sgn b)
no goals