An PDP-1 hack probably deliberately omitted (e.g., from http://inwap.com/pdp10/hbaker/hakmem/hacks.html), but perhaps worth preserving: It was an 18 bit, 4K (!) machine with a 6 bit character code (FIO-DEC), and most of the printouts were three characters. E.g., in the assembler, usw = undefined symbol in word mce = macro capacity exceeded, and in Samson's music compiler, mts = measure too short agm = argument greedily masticates To type out the three characters in the AC, lio asa /load IO rcl 6s /rotate combined left 6 bits tyo asa, sas asa /skip if AC same as . jmp .-3 This was safe because the 6-bit order code for sas (not indirect) was an illegal FIO-DEC character (which actually jammed the Soroban typewriter?). Also, a most regrettable typo ruins a spectacular mate in 3: http://www.inwap.com/pdp10/hbaker/hakmem/games.html ITEM 70: A neat chess problem, swiped from "Chess for Fun and Chess for Blood", by Edward Lasker: white: pawns at QN3 and KN7, knight at QN4, bishop at KB7, king at QB2; (NO, the B should be KB8!) black: pawn at QN3, king at QR6. White mates in three moves.