The Tower of Hanoi (also called the Tower of Brahma or Lucas' Tower
and sometimes pluralized) is a mathematical game or puzzle. It
consists of three rods and a number of disks of different sizes,
which can slide onto any rod. The puzzle starts with the disks in
a neat stack in ascending order of size on one rod, the smallest
at the top, thus making a conical shape.
The objective of the puzzle is to move the entire stack to another
rod, obeying the following simple rules:

• Only one disk can be moved at a time.

• Each move consists of taking the upper disk from one of the

stacks and placing it on top of another stack.
• No disk may be placed on top of a smaller disk.

With 3 disks, the puzzle can be solved in 7 moves. The minimal
number of moves required to solve a Tower of Hanoi puzzle is
2^n-1, where n is the number of disks.

Taken from https://en.m.wikipedia.org/wiki/Tower*of*Hanoi

`~~~``{ 'Num 'From 'To 'Via } [ var ] a:for-each `
` `
`:set !Via !To !From !Num ; `
`:display @To @From 'Move_a_ring_from_%n_to_%n\n s:format s:put ; `
` `
`:hanoi (num,from,to,via-) `
` set @Num n:-zero? `
` [ @Num @From @To @Via `
` @Num n:dec @From @Via @To hanoi set display `
` @Num n:dec @Via @To @From hanoi ] if ; `
` `
`#3 #1 #3 #2 hanoi nl `
`~~~`