 For example, the "full employment theorem for compiler writers" states that there is no such thing as a provably perfect size-optimizing compiler, as such a proof for the compiler would have to detect non-terminating computations and reduce them to a one-instruction infinite loop.Thus, the existence of a provably perfect size-optimizing compiler would imply a solution to the halting problem, which cannot exist.This also implies that there may always be a better compiler since the proof that one has the best compiler cannot exist.