Napoleon's problem

Given a circle and its center, divide the circle into four equal arcs using only a compass.

`BOc`	draw the circle around B through O
`BOAc`	draw the circle around B with radius \|OA\|
`OApB`	name B any new point of circle OA
`OAxBOC`	walk clockwise around OA from the point facing the center of BO; name C the first new point where they cross
`ABCD`	last word: the four answer points