This fact significantly helps for proving a
function f to be invertible by showing that f is one-one and onto, specially when the
actual inverse of f is not to be determined Example 17 Let f : N → Y be a function defined as f (x) = 4x + 3, where,
Y = {y ∈ N: y = 4x + 3 for some x ∈ N} Show that f is invertible Find the inverse