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Subj:.....Primitive Railroading Problem (S620)           From the book             "Mathematical Puzzles of Sam Loyd"              Edited by Martin Gardner              From: Dover Publications in 1959   Find the simplest method by which the trains can pass. In this specimen of primitive railroading we have an engine and four cars meeting an engine with three cars. The problem is to ascertain the most expeditious way of passing the two trains by means of the side-track, which is only large enough to hold one engine or one car at a time. No ropes, poles or flying switches are to be used, and it is understood that a car cannot be connected to the front of an engine.  How many times is it necessary to back or reverse the directions of the engines to accomplish the feat, each reversal of an engine being counted as a move in the solution?

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