Modularity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 Michael Abbott, Neil Ghani, and Christoph L?uth Union of Equational Theories: An Algebraic Approach . . . . . . . . . . . . . . . . . . 61 Piotr Hoffman Equivariant Unification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 James Cheney Faster Basic Syntactic Mutation with Sorts for Some Separable Equational Theories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 Christopher Lynch and Barbara Morawska Unification in a Class of Permutative Theories . . . . . . . . . . . . . . . . . . . . . . . . . 105 Thierry Boy de la Tour and Mnacho Echenim Dependency Pairs for Simply Typed Term Rewriting . . . . . . . . . . . . . . . . . . . 120 Takahito Aoto and Toshiyuki Yamada Universal Algebra for Termination of Higher-Order Rewriting. . . . . . . . . . . . 135 Makoto Hamana Quasi-interpretations and Small Space Bounds . . . . . ...