Pythagoras Tree represents Pythagoras Theorem: 'The square on the hypotenuse is equal to the sum of the squares on the other two sides.' In this case, the 'squares on the other two sides' are equal so, in knitting terms, that means that each small square has exactly half as many stitches to knit as the large square on the same triangle. There are five sizes of square, getting ever smaller. The design is like a fractal as the same pattern is repeated at smaller sizes.
The afghan is worked entirely in garter stitch with the squares and triangles being knitted first and the background knitted on afterwards. The booklet includes a colouring sheet where you can plan your own colour combination. I used Aran yarn. It will also work with other thicknesses but the overall size may change.
The original afghan was bought by the Mathematics Collection of the London Science Museum.