I am working on a piece of encoding that finds the cell with the lowest coordinates in a grid. This cell will be used as a starting point for a path. Cells are defined with predicate cell(X,Y).
isLower(X,Y,F,G) :- cell(X,Y), cell(F,G), X<=F, Y<=G.
first(X,Y) :- cell(X,Y), not black(X,Y), cell(F,G), not black(F,G), cell(A,B), not black(A,B), isLower(X,Y,F,G), not isLower(A,B,X,Y).
I want to have only one first cell. My problem is that ASP starts giving me a bunch of cells, because first(X,Y) is a predicate and ASP will try to produce as many as it can.
How do I tell the program that it is supposed to find only the lowest element (i.e. the cell with the smallest coordinates)? How can I force it to be only ONE cell?
It is still unclear what exactly you want to achieve, but in case that cell/2 are facts, i would recommend a rule like:
first(X',Y') :- (X',Y') = #min {(X,Y) : cell(X,Y)}.