Corresponding author: Karl Strötmann (

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This paper addresses the correctness problem of an algorithm solving the constrained shortest path problem. We define an abstract, nondeterministic form of the algorithm and prove its correctness from a few simple axioms. We then define a sequence of natural refinements which can be proved to be correct and lead from the abstract algorithm to an efficient implementation due to Ulrich Lauther [Lauther 1996] and based on [Desrosiers et al. 1995]. Along the way, we also show that the abstract algorithm can be regarded as a natural extension of Moore s algorithm [Moore 1957] for solving the shortest path problem.