An extension of the Fukaya-Kato method

In a groundbreaking paper, T. Fukaya and K. Kato proved a slight weakening of a conjecture of the author’s relating modular symbols and cup products of cyclotomic units under an assumption that a Kubota-Leopoldt p-adic L-function has no multiple zeros. This article describes a refinement of their method that sheds light on the role of the p-adic L-function.