"Let f : X→ Y and g : Y→ Z are invertible functions then

gof is not invertible "gof is invertible and (gof) -1 ≠ f-1og -1 gof is invertible and (gof) -1 = f-1og -1 gof is not onto

gof is invertible and (gof) -1 = f-1og -1

Show that (gof) (f -1 o g-1) (x) = x.