Lucid, a Nonprocedural Language with Iteration
Lucid is a formal system in which programs
can be written and proofs of programs carried out. 
 The proofs are particularly easy to follow and straightforward
to produce because the statements in 
a Lucid program are simply axioms from which the proof
proceeds by (almost) conventional logical reasoning, 
with the help of a few axioms and rules of inference
for the special Lucid functions.  As a programming 
language, Lucid is unconventional because, among other
things, the order of statements is irrelevant 
and assignment statements are equations.  Nevertheless,
Lucid programs need not look much different than 
iterative programs in a conventional structured programming
language using assignment and conditional 
statements and loops.
CACM July, 1977
Ashcrof, E. A.
Wadge, W. W.
