An initial position of Toads & Frogs is a horizontal line of boxes,
some of which are occupied by a toad, some by a frog, and some empty.
Left move one toad to the right, or can leap one frog by moving two to
the right. Similarly, Right moves frogs left.
To enter a position, type toads , followed by a line of
characters. Type a t for a toad, f for a frog, space for an empty box,
and | for a wall. (Toads nor frogs can pass through walls.)
For example,
> toads
|t f|
returns *. Left could move a toad to the right to | tf| = 0 and from
this position, only Right has a move to |ft | = 1 from which Left has
a move to |f t| = 0.
For another example,
|t tf| = 1/2
Left moves to | ttf| = 0, while Right moves to |tft | = 1.
Toads & Frogs was implemented by Jeff Erickson.