representation of electrical circuits (paper)
In 1971, near the end of his first year at Harvard, he became a programmer at the MIT Artificial Intelligence Laboratory [...]


While working (starting in 1975) as a research assistant at MIT under Gerry Sussman,[18] Stallman published a paper (with Sussman) in 1977 on an AI truth maintenance system, called dependency-directed backtracking.[22] This paper was an early work on the problem of intelligent backtracking in constraint satisfaction problems. As of 2009, the technique Stallman and Sussman introduced is still the most general and powerful form of intelligent backtracking.[23] The technique of constraint recording, wherein partial results of a search are recorded for later reuse, was also introduced in this paper.[23]

Full text PDF of bolded paper: http://dspace.mit.edu/bitstream/handle/1721.1/6255/AIM-380.pdf
As Renan also mentioned in the comments, there is also a slightly older paper: Heuristic techniques in computer-aided circuit analysis (full text PDF).