U = Adam is Ugly
D = Adam is Dumb
In a sentence of sentence logic:
This means that it is NOT the case that Adam is BOTH dumb AND ugly. He COULD be either one, but not BOTH at the same time. It rules out the case that he is both dumb AND ugly together.
I actually used a truth table to figure out the equivalent expression since I was initially unsure (spreadsheets are really good for truth tables). Negation can be a bit trick to keep straight.
So the equivalent expression to ∼(D&U) is ∼Dv∼U.