In your context, you need to mention what P & D actually are (what mathematical structures are they?), so as to check if D can ever be unbounded or P can ever be infeasible. So, it pretty much depends on the context in which this's said, since both appear to be logically (!) correct. If negation of proposition is true, proposition is false. If proposition is true, it's negation is false OR If a proposition is false, it's negation is true & vice versa. Im also using the more formal '' instead of '', and. There're some cases, where 'vice versa' may mean what you doubt it means, like in the following example: From the English Cambridge dictionary, 'vice versa' is defined as: used to say that what you have just said is also true in the opposite order. (truth of p implies truth of q) AND (truth of q implies truth of p). ' and vice versa' in the language of logic means p q is true, which is actually the case, when both p->q & q->p are true. NOTE: p & q here are logical statements ( propositions, having fixed truth values).So in this example of yours

Whats vice versa