"The Axiom of Choice is obviously true, the well-ordering principle obviously false, and who can tell about Zorn's lemma?" — Jerry Bona
This is a joke: although the three are all mathematically equivalent, most mathematicians find the axiom of choice to be intuitive, the well-ordering principle to be counterintuitive, and Zorn's lemma to be too complex for any intuition.
What's yellow and equivalent to the axiom of choice?
The axiom of choice is actually equivalent to Zorn's lemma. Acolytes at the altar of mathematics are inculcated with this fundamental truth before admission to the priesthood. The problem is that since both the axiom of choice and Zorn's lemma are so deep and abstract, it takes years before the full significance of their equivalence can be appreciated.
CRC refers to the "CRC Standard Mathematical Tables and Formulae", a kind of handbook for mathematicians and engineers published by the CRC press. Although CRC press has by now been vacuumed up as part of some larger publishing conglomerate, its origins were in the Chemical and Rubber Company, from whose name its initials are derived.
A physicist, an engineer and a mathematician were all in a hotel sleeping when a fire broke out in their respective rooms.
The physicist woke up, saw the fire, ran over to his desk, pulled out his CRC, and began working out all sorts of fluid dynamics equations. After a couple minutes, he threw down his pencil, got a graduated cylinder out of his suitcase, and measured out a precise amount of water. He threw it on the fire, extinguishing it, with not a drop wasted, and went back to sleep.
The engineer woke up, saw the fire, ran into the bathroom, turned on the faucets full-blast, flooding out the entire apartment, which put out the fire, and went back to sleep.
The mathematician woke up, saw the fire, ran over to his desk, began working through theorems, lemmas, hypotheses , you -name-it, and after a few minutes, put down his pencil triumphantly and exclaimed, "I have *proven* that I *can* put the fire out!" He then went back to sleep.