Cardinality of Set of All Mappings/Examples/3 Elements to 2 Elements

Example of Cardinality of Set of All Mappings
Let $S = \set {1, 2, 3}$.

Let $T = \set {a, b}$.

Then the mappings from $S$ to $T$ in two-row notation are:


 * $\dbinom {1 \ 2 \ 3} {a \ a \ a}, \dbinom {1 \ 2 \ 3} {a \ a \ b}, \dbinom {1 \ 2 \ 3} {a \ b \ a}, \dbinom {1 \ 2 \ 3} {a \ b \ b}, \dbinom {1 \ 2 \ 3} {b \ a \ a}, \dbinom {1 \ 2 \ 3} {b \ a \ b}, \dbinom {1 \ 2 \ 3} {b \ b \ a}, \dbinom {1 \ 2 \ 3} {b \ b \ b}$

a total of $2^3 = 8$.

All but the first and last are surjections.

None are injections.