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这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

If you click with mouse button 1
on a (destination) square then the following may happen.

If
 - the destination square is on the same row or column as glenda, and
 - there is a ball next to glenda
   (in the direction of the destination square), and
 - all squares between the ball and the destination square
   (where glenda will move) are empty, and
 - the square next to the destination square where glenda will
   push the ball is empty too, 
then glenda will move to the destination square, pushing the
ball while moving.

Otherwise, if glenda can go to the destination square
without touching anything, it will do so.

Otherwise, nothing will happen.

The breadth-first search algorithm should find a fast route.
it can be seen in action by toggling the 'animate'
entry in the button 3 menu.