One-to-one means that F(s) = F(s') only happens if s=s'.

Onto means that for each t in the target space T there is an s such that F(s)=t.

The necessity that F(s) not have 2 values is required for F to be a function.

I knew I should check. (It's been far too long since I dealt with them separately... mostly what matters is whether a given function is a permutation or not.) Anyway, my point that ++ is not onto and therefore not reversible is still valid, even though I mixed up one-to-one pretty badly.

$;=sub{$/};@;=map{my($a,$b)=($_,$;);$;=sub{$a.$b->()}}
split//,".rekcah lreP rehtona tsuJ";$\=$ ;->();print$/
[download]