Guy Steele in the Hackers & Painters/XP thread on ll1-discuss:
Posted by jjwiseman at May 16, 2003 09:15 AM
FWIW, the early Scheme interpreters were the result of pair programming (Sussman and I working together, and often trading places at the keyboard). The early Scheme papers were the result of pair writing, where if a paragraph wasn't flowing smoothly from one guy's fingers then the other would jump in with a reformulated sentence.
And the first TECO macro to pretty-print Lisp code for EMACS (including making decisions about line breaks, not just how much to indent each line) was the result of a ten-hour pair-programming session with me at the keyboard and Stallman at my right elbow.