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    I've got a question: Suppose Jim is at (0,0), the mirror is at (0,2) and the wall goes from (0,1) to (1,1); now, can Jim cast the beam or not? It depends: If the wall is an open line segment (doesn't include the endpoints) the answer is YES, while if it's close, the answer is NO.

    Do we know which case we're dealing with?