The number of injective functions from a set X containing m elements to a set Y containing n elements  for m>n is:

function from X to Y then n≥ where n=n(X)and n=n(Y) The number of injective functions from X to Y is n(n−1)(n−2)…(n−m+1)=nPmAs m>n, there does not exist any injective function from x to y