Clarify the Black Box rules slightly.

Chris Boyle points out that two of the rules are implicitly intended
to be read as only applying if a previous rule hadn't already decided
what would happen, and suggested that since not all readers infer that
priority order, it would be better to explicitly make them mutually
exclusive so that there can be no confusion about which one applies.

diff --git a/puzzles.but b/puzzles.but
index 523574c33d50630afe4e178207efedee01cba689..2508fe3337f2faeecfff4086a67e1a8e121ec380 100644 (file)
--- a/puzzles.but
+++ b/puzzles.but
@@ -1553,11 +1553,11 @@ affected by balls in one of the following ways:
    re-emerge. This includes beams that meet a ball on the first rank
    of the arena.
 
-\b A beam with a ball to its front-left square gets deflected 90 degrees
-   to the right.
+\b A beam with a ball in its front-left square and no ball ahead of it
+   gets deflected 90 degrees to the right.
 
-\b A beam with a ball to its front-right square gets similarly deflected 
-   to the left. 
+\b A beam with a ball in its front-right square and no ball ahead of
+   it gets similarly deflected to the left.
 
 \b A beam that would re-emerge from its entry location is considered to be
    \q{reflected}.