Products on Tor

In 1974 work establishing the collapse of certain Eilenberg-Moore spectral sequences, Munkholm constructs, in passing, a bilinear multiplication operation on Tor of a triple of $A_\infty$-algebras. In 2020, the present author, pursuing a multiplicative collapse result extending Munkholm's, studied a variant of this product, without actually showing it agrees with Munkholm's. In 2019, Franz had defined a weak product on the two-sided bar construction of a triple of $A_\infty$-algebras under similar hypotheses, with which this author proved a related collapse result, but without investigating the properties of the induced product on Tor. The present work demonstrates that the two products on Tor agree and are induced by the product of Franz.