Play

This thing displayed at the center of the screen is the target. Numbers that are rushing at the bottom left are a counter. You figure what happens when it reachs zero. The icon at the bottom right make you leave the target and see your working area. In the other way round, you can see the target with another icon to see how close you are from the target.

At the top of the screen are a row of primitives spaced with unions operators. Remeber that union is written ∪, intersection is written ∩, and minus - (just to be sure).

By dragging the mouse on the window, you can turn the view around the shape.

Go ahead, and when you are done click on the icon.

Now, you can only see the union of all the primitives, centered. You have to figure out how to do the targetted shape with them.

You can select any formula's element by clicking or dragging on the top window. By selecting a primitive on the formula, some arrows apears that can be used (if you click on them) to move the primitive. If you then again click on the primitive of the formula, you can switch between arrows that turn/translate the primitive.

By clicking an operator, you change it.

You can also sort out some elements of the formula by selecting then and pasting with right mouse button.

Or you can (un)parentheses the selection by using an icon or right-clicking on the selection.

With this in mind, try to build the target. When you are satisfied with the result, click on the check icon at bottom rightmost. Primitives will let you know if you made something wrong. Seeing in "CSG space" is not easy. Good luck.