- For every nontrivial $A,B\in R$, $A\le_m B$
- For every nontrivial $A,B\in RE$, $A\le_m B$
trivial set is the empty-set or $\Sigma^*$.
So basically the question is if for every two nontrivial sets there is a computable function from $A$ to $B$.
I'd be glad to get hint/guidance since I'm kinda stuck and not sure how to attack this problem.