Paper/Laws of programming

Hoare, C. A. R.; Hayes, I. J.; He, Jifeng; Morgan, C. C.; Roscoe, A. W.; Sanders, J. W.; Sorensen, I. H.; Spivey, J. M.; Sufrin, B. A. (Aug 1987). "Laws of Programming" (PDF). 30 (8). local page: ACM. 

Abstract

A complete set of algebraic laws is given for Dijkstra's nondeterministic sequential programming language. Iteration and recursion are explained in terms of Scott's domain theory as fixed points of continuous functionals. A calculus analogous to weakest preconditions is suggested as an aid to deriving programs from their specifications.

One should also watch Dana Scott's lectures on $\lambda$ calculus.