Classify the below as a function, one$-$to$-$one, onto, or none if f : X $$ Y $,$ X $=\{$a$,$ b$,$ c$,$ d$,$ e$\},$ and

Y $=\{1,2,3,4,5\}.$ Explain why and reference the definitions from above.

x f $($x$)$

a $1$

b $2$

c $3$

d $4$

e $5$