Thread: Combinations?

If X is a set containing n elements and Y is a set containing m elements, how many functions are there from X to Y? How many of these functions are one-to-one?

Originally Posted by fardeen_gen

If X is a set containing n elements and Y is a set containing m elements, how many functions are there from X to Y? How many of these functions are one-to-one?

For every element in X, I just need to associate an element of Y(for which I have m choices). Thus functions.

For one-one functions, For every element in X, I need to associate only one element of Y. Thus for the first one I have, m choices. Then for the second element, I have m-1 choices and so on. So it is

And for your information, there are injective functions from X to Y.

Originally Posted by Moo

And for your information, there are injective functions from X to Y.

Isnt that the same as ?

Yes, it's the same.
But that's what I had in my notes. (they're from last year, so I don't have the proofs...)


I'm wondering... If , is it possible to have one-to-one functions from X to Y ?

We may consider that we're dealing with functions whose domain is X, and whose range is Y. In which case, there is no one-to-one functions


If , the number of bijective functions is n!

Originally Posted by fardeen_gen

If X is a set containing n elements and Y is a set containing m elements, how many functions are there from X to Y? How many of these functions are one-to-one?

O.K fardeen_gen.
Do you know the number of ONTO functions from X to Y