Let, f : ℝ → ℝ +
f ( x ) = x 2
Let, $f’: R^+ \rightarrow R^+$ f’ ( x ) = x 2
And, taking g : ℝ + → ℝ + g ( y ) = y ,where, g ≡ f ′ - 1
f ′ - 1 : ℝ + → ℝ +
f ′ - 1 ( y ) = y .