Sonneveld's Color 4-Piece retailer Cube

This is a reproduction of Dic Sonneveld's "Four Piece Cube" puzzle. It's an elegant puzzle I've enjoyed for years and Dic has given me his permission to reproduce it.

The puzzle consists of two copies of two different pieces (for a total of four pieces, hence the name) that form a cube, 1 ½ inches on a side. Ordering this item gets you all four pieces in red, green, blue, and yellow as shown in the picture. If you want to retailer order the pieces in different colors, they're available (and at a lower price) at my Shapeways store (https://www.shapeways.com/product/HA4FWPS6D/sonneveld-s-4-piece-cube-all-pieces) and at my i.materialise store (https://i.materialise.com/en/shop/item/sonneveld-s-4-piece-cube-all-pieces).

If you want all four pieces in plain white, they're also available on my Shapeways and i.materialise stores, and sometimes here on my Etsy store.

Note that you will be getting the puzzle in an unassembled state so the challenge is to figure out how to put the pieces together. :) I also include a clear plastic box that fits the assembled puzzle exactly.