Proofs and the future affecting the past

Retrocausality is where the future affects the past. I've noticed before that this happens in novels all the time: events happen early in the novel so that other events later in the novel are possible. I noticed today that the same thing happens in proofs: the mathematician often proves theorems he will need to make use of later to prove what he really wants. It's just like how Q gives Bond the very gadgets he will later need to escape from this mission's particular trap.