Ellis Cohen Problems, Mechanisms, and Solutions Degree Type: Ph.D. in Computer Science Advisor(s): William Wulf Graduated: August 1976 Abstract: This thesis formalizes the notions problem, mechanism and solution, and shows how such a formalization is useful in describing problems and proving the correctness of solutions to them in computational systems. Mechanisms are formally defined as mappings layers between two computational systems. They provide natural models for protection, synchronization, and sequential and parallel control mechanisms. Certain algebraic properties of mechanisms are discussed these correspond to properties one would ordinarily consider in studying the mechanisms listed above. Thesis Committee: William Wulf (Chair) Joseph Traub, Head, Computer Science Department