Good point. I don't think the puzzles do this and if they would, I would run a pre-solve pass over the puzzle first to flood fill such horseless pockets up with water, no?
Like the other comment suggested, running a loop where you keep adding constraints that eliminate invalid solutions will probably work for any puzzle that a human would want to solve.
Score: 7
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reachable(x,y,t) = reachable(nx,ny,t-1)
Score: 2
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