Mystery Master	Analysis of The Smith-Jones-Robinson Classic	Member

This two-star logic puzzle has 4 noun types, 3 nouns per type, 1 link, 4 facts, and 1 rule that includes a trigger. It needs only 54 marks and 6 grids. Though the puzzle is not hard, it is somewhat ambiguous. In most puzzles, you assume something is possible until you determine it is not. For example, the workers could be addressed as "Mr. Smith", "Mr. Robinson", and "Mr. Jones", but not on this train - formality is only for the passengers. Also, Chicago and Detroit were given as two of the cities, but not the city between them, so I called it "Halfway". And keep in mind that the puzzle is asking for the name of the engineer. So, to make things clearer:

• Exactly one worker and one businessman lives in each city.
• In clue 4, the brakeman's nearest neighbor is the businessman who lives in the brakeman's city.
• For clues 3 and 4, $20,000 is not exactly divisible by 3 ($6,666.66...). This is how we determined fact 3.

• Mr. Robinson lives in Detroit. (clue 1)
• The brakeman lives in Halfway. (clue 2)
• The brakeman's neighbor is not Mr. Jones. (clues 3,4)
• Smith is not the fireman. (clue 5)

• The businessman with the same name as the brakeman lives in Chicago. (clue 6)

Looking at the rule, there are two triggers we could implement (only the second one is implemented).

• If we know the name of the brakeman, then we know the name of the businessman.
• If we know the name of the businessman, then we know the name of the brakeman.

No Assumptions

If we solve the puzzle without assumptions, we find 38/54 marks, 10/18 pairs, and all 4 facts have been fully examined.

Assumptions

The goal is to find the name of the engineer. If the program uses assumptions to solve the puzzle, it will find two solutions, with 1 and 2 assumptions, but both will have the engineer is Smith. The program only needs those 2 assumptions to exhaust all possible combinations.

Like I said at the beginning, this puzzle is ambiguous. There are two solutions, but they both answer the question "Who is the engineer?" If the puzzle had the additional clue "No two people with the same name live in the same city.", then the puzzle would have only one solution.