The first elements of the pairs given all are from A (l, m, n). The second all are from B (30, 20, 10). And this is good ("from set A to set B").

Also, there are no pairs for which the first element are coincide but second are not, so the correspondence is single-valued. And this is also good.

The only problem I see is that there is no pair for o from the set A. So the function is defined only at a subset of A, not at entire A. So my answer is NO but please look at you definition of "a function".