Arnold M. Zwicky, A double regularity in the acquisition of English verb morphology. Papers in Linguistics 3.3.411-8 (1970). Also in OSU WPL 4.142-8 (1970). From OSU Working Papers in Linguistics No. 4: Papers by Gaberell Drachman, Mary Louise Edwards, Charles J. Fillmore, Gregory Lee, Patricia Lee, Ilse Lehiste, and Arnold M. Zwicky