Unifying Theories of Undefinedness in UTP -- Unifying Theories of Programming with Monads -- Circus Time with Reactive Designs -- Algebra Unifies Operational Calculi -- A Probabilistic Theory of Designs Based on Distributions -- The Logic of U•(TP)2 -- Conscriptions: A New Relational Model for Sequential Computations -- Mechanical Approach to Linking Operational Semantics and Algebraic Semantics for Verilog Using Maude -- Unifying Operational Semantics with Algebraic Semantics for Instantaneous Reactions -- Higher-Order UTP for a Theory of Methods -- Denotational Semantics for a Probabilistic Timed Shared-Variable Language.

This book constitutes the refereed proceedings of the 4th International Symposium on Unifying Theories of Programming, UTP 2012, held in Paris, France, in August 2012, co-located with the 18th International Symposium on Formal Methods, FM 2012. The 8 revised full papers presented together with 2 invited talks and one invited lecture were carefully reviewed and selected from 13 submissions.