Mathematical proofs are used to prove the cor­rect­ness of formulas and as­sumed facts. Sev­er­al basic procedures and ways of veri­fy­ing mathematical cor­rect­ness are in use, all of which follow a fixed scheme.

For the proof of the irrationality of the square root of 2 dif­fer­ent proofs exist. This article explains the indirect proof vari­ant in detail and introduces one of the possible short spell­ings in mathematical notation. Exercises with solutions con­soli­date what has been learned. 13 pages:   A4  •  A4 duplex  •  US-Let­ter  •  US-Letter duplex