zebra-puzzle

I'm reading the "7 Languages in 7 Days"-book, and have reached the Prolog chapter. As a learning exercises I'm trying to solve some textual logic puzzles. The puzzle goes as follow: Five sisters all have their birthday in a different month and each on a different day of the week. Using the clues below, determine the month and day of the week each sister's birthday falls. Paula was born in March but not on Saturday. Abigail's birthday was not on Friday or Wednesday. The girl whose birthday is on Monday was born earlier in the year than Brenda and Mary. Tara wasn't born in February and her

I am trying to solve Einstein Riddle in Prolog. I am having a difficulty with the program I wrote, the basic method was to add all constraints and let Prolog figure out the only possible solutions. The problem is that Prolog finds 0 solutions. I have isolated the constraint that makes the program go from a given solution to no solutions, but I don't understand why. /*There are five houses*/ exists(A, list(A,_,_,_,_)). exists(A, list(_,A,_,_,_)). exists(A, list(_,_,A,_,_)). exists(A, list(_,_,_,A,_)). exists(A, list(_,_,_,_,A)). middle_house(A, list(_,_,A,_,_)). first_house(A, list(A,_,_,_,_)).

I have been given an exercise to solve the zebra puzzle using a constraint solver of my choice, and I tried it using the Prolog clpfd library . I am aware that there are other more idiomatic ways to solve this problem in Prolog, but this question is specifically about the clpfd package! So the specific variation of the puzzle (given that there are many of them) I'm trying to solve is this one: There are five houses The Englishman lives in the red house The Swedish own a dog The Danish likes to drink tea The green house is left to the white house The owner of the green house drinks coffee The