How Dennis realized he had `invented' $L_\infty$-algebras a.k.a.   strongly homotopy Lie algebras
  This is my attempt to rediscover how Dennis realized that he had discovered/invented $L_\infty$-algebras a.k.a. strongly homotopy Lie algebras before my colleagues and I defined them. 
Jim Stasheff
math.AT math.HO