Abstract Since logic programs are executable specifications, the main concern of logic programming, producing efficient programs, is tangential to the mainstream of formal methods. A fashionable automatic transformation technique for producing efficient programs, partial evaluation, applied to the concurrent logic programming language Parlog is discussed.

When repeatedly editing a text file, one is often faced with a choice of keeping previous generations for backup or deleting previous generations to reduce storage requirements. Since one generation of a text file is often very similar to the previous generation, the above conflict can often be resolved by sharing much of the common information. We propose using a tree structure to represent a text file. Common subtrees can be shared. Results of an experiment with one file are reported.

A virtual tree machine consists of a fixed finite network of processors together with a suitable algorithm for deciding when and where to solve each subproblem.