The following applet explains the Fortress Problem and the steps used to solve it. Please refer to the other pages of this site.
This applet uses several pieces of code provided by Joe O'Rourke and has a Help facility. It should be self-explanatory. Have fun!
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There are two cases not supported in the "Point Guards" solution:
1) When the convex hull is not two-colorable (it has an odd number of vertices),
and there is no pocket whose lid's apex is visible from either L or R.
In this case, the applet may fail to find an appropriate guard. 2) When
there are two uppermost points and two lowermost points (A and B are not