a\ Accepted by 4

Computer Science The Ether language, a language for parallel problem solving, is used as an implementational vehicle for two systems. Several aspects of these systems are novel and depend on the presence of parallelism. One of these is a system that solves cryptarithmetic puzzles. This system is capable of pursuing several alternative hypotheses about assignments of letters to digits in parallel. The resources given to these various activities can be changed asynchronously with their running. Strategies for resource allocation are described. It is argued that parallel search offers greater flexibility in controlling the search process than can classical tree search algorithms. The second is a program synthesis system that takes as input a description of the relationship between inputs and output of a Lisp function in a variant of first order predicate logic. The system synthesizes a Lisp program from this description. The system was designed to test the notion of pursuing multiple implementation strategies in parallel with skeptic strategies. The skeptic strategies attempt to show that certain proposed implementation strategies cannot possibly work. If these succeed, work on the successfully refuted implementation strategy is halted. Sometimes one skeptic can simultaneously refut