the plate trick, also known as Feynman’s plate trick, Dirac’s belt trick, Dirac’s string trick, Balinese cup trick, spinor spanner, Bredon high-five, or quaternionic handshake, is any of several particular physical demonstrations of the mathematical theorem that SU(2) double-covers SO(3). The usual demonstration, as indicated by the name, is to hold a plate on one’s flat palm, then perform two subsequent rotations of the arm holding the plate, which results in the original position. In the cup variant, supposedly inspired by a Balinese candle dance, an open cup of water or wine is held in ones hand and rotated 720 degrees, or any multiple thereof, without spilling the liquid or loosening ones grip on the cup.

A prime number p is a Sophie Germain prime if 2p 1 is also prime

Sergeyev begins by adding a new axiom to the axiom of real numbers, which he calls the infinite unit axiom. This introduces grossone–the infinite unit.

Because it is governed by the other axioms of real numbers, grossone behaves much like one too. So it’s possible to multiply grossone, divide it, add to it and subtract from it, just as is possible with other real numbers.