Fermat's theorem was a mathematical statement. The Eleventh Doctor used a proof of it to convince a body of geniuses they should take his advice about how to save the world from annihilation by the Atraxi. He uploaded the proof — which the Doctor called "the real one, never been seen before" — to a secure video conference from a laptop computer in Leadworth. Simultaneously, he muttered an acknowledgment to the originator of the theorem, Fermat, and mentioned that Evariste got killed in a duel before he could write down his own proof. He claimed responsibility for the death of the latter, saying that it had only happened because he had slept in that morning. (TV: The Eleventh Hour)