Patented by F. Gruber 1993, Copyright Interconcept GmbH.
(left: plastic, 3 inches, 3-wing version, red / blue / yellow;
right: plastic, 4-wing version, black / white / blue / green / red / yellow / gray / purple)
The basic operation is to make two of the semi-circles co-planar and then rotate the resulting circle 90 degrees.
After mixing up,
restore the puzzle to a fun pattern.
Below are the directions that were sold with the 3-wing version.
presents a solution.
from: www.uspto.gov - patent no. 5,267,731