l:("Click on any of the pieces next to the space, and"
   "that piece will slide over the space.  Continue  "
   "this until the pieces are arranged in numerical  "
   "order from upper-left to lower-right.            ")
l.[`l`e]:`,0

m:4 4#2$'(1+15_draw-15),0N
m.[`l`x`k]:`,15,,"move _i"

move:{if[1=+/_abs x-p:,/(&|/)'(+:;::)@\:&/''m=" ";(p;x).[`m;;:;]'(m . x;"  ")]}

Dismiss:"`hide$`.k"
Code:"`show$0:`puzzle.k;"
Dismiss..c:Code..c:`button

.k..l:"15-Puzzle Demonstration"
.k..a:`l,`m,,`Dismiss`Code
`show$`.k