Summary: HOOTS'00 to appear
E#cient Substitution in Hoare Logic
Andrew W. Appel Kedar N. Swadi
Department of Computer Science
Princeton, NJ, U.S.A.
Substitution plays an important role in Hoare Logic, as it is used in interpreting
assignments. When writing a computerbased realization of Hoare Logic, it is there
fore important to choose a good implementation for it. In this paper we compare
di#erent definitions and implementations of substitution in a logical framework, in
an e#ort to maximize e#ciency.
We start by defining substitution as a logical formula. In a conventional ap
proach, this is done by specifying the syntactic changes substitution performs on
expressions. We choose instead a semantic definition that describes the behavioral
relation between the original expression and its substituted counterpart.
Next, we use this semantic definition as an abstract specification, and compare