Add X as a hypothesis, where X is not known to be either true or false.
Some results in theoretical computer science and mathematics, and particularly in computational complexity, are conditional on some result that is not known to be true. An example is Ladner's Theorem, which says that if P≠NP, then there is an infinite hierarchy of complexity classes between P and the NP-complete problems. If someone were to prove that P=NP, then Ladner's Theorem would become uninteresting, since anything can be deduced from a false premise. However, if P≠NP were to be proved, then the conclusion of Ladner's Theorem would be unconditionally true.