Four puzzle pieces, also known as the T puzzle, is a traditional intellectual toy similar to Tangram. The four-piece puzzle consists of 4 irregular shapes broken down into a rectangle (the capital "一" in the puzzle). There are one right-angled trapezoid of different sizes, one isosceles right-angled triangle, and one concave pentagon. In addition to the right angles, the interior angles of these polygons also have angles of 45º, 135º, and 270º. It’s said that it’s the hardest to put the four-piece puzzle into a capital "T" shape.