Mairson, Harry G. (14 September 1992). "A simple proof of a theorem of Statman". Theoretical Computer Science. 103 (2): 387–394. doi:10.1016/0304-3975(92)90020-G. ISSN0304-3975.
Goldfarb, Warren D. (1 January 1981). "The undecidability of the second-order unification problem". Theoretical Computer Science. 13 (2): 225–230. doi:10.1016/0304-3975(81)90040-2. ISSN0304-3975.
Mairson, Harry G. (14 September 1992). "A simple proof of a theorem of Statman". Theoretical Computer Science. 103 (2): 387–394. doi:10.1016/0304-3975(92)90020-G. ISSN0304-3975.
Goldfarb, Warren D. (1 January 1981). "The undecidability of the second-order unification problem". Theoretical Computer Science. 13 (2): 225–230. doi:10.1016/0304-3975(81)90040-2. ISSN0304-3975.