This volume contains the papers presented at the 4th Fuji International S- posium on Functional and Logic Programming (FLOPS 99) held in Tsukuba, Japan, November 11 13, 1999, and hosted by the Electrotechnical Laboratory (ETL). FLOPS is a forum for presenting and discussing all issues concerning functional programming, logic programming, and their integration. The sym- sium takes place about every 1.5 years in Japan. Previous FLOPS meetings were held in Fuji Susuno (1995), Shonan Village (1996), and Kyoto (1998). 1 There were 51 submissions from Austria ( ), Belgium (2), Brazil(3), China 3 3...

This Festschrift is dedicated to Jan Willem Klop on the occasion of his 60th birthdayon December 19,2005.Its focus is on the lambda calculus, term rewr- ing and process algebra, the ?elds where Jan Willem has made fundamental contributions. Without attempting to give a balanced account of Jan Willem s scienti?c achievements, we recall three accomplishments from the early years of his career that especially stand out. The ?rst is his counterexample showing that the extension of the lambda calculus with surjective pairing lacks the Church Rosserproperty, or, in modern terminology, is not...