/sci/ - Science & Math

>>12615752
Now for the actual proof:
There are four corners of the 5x5 grid: A1, A4, E1, and E4. By Lemma 1, a part cannot occupy more than one corner. Then three corners must be occupied by three different parts, and the fourth corner must be the square removed. Without loss of generality, the squares may be coloured like the picture, with red, green, and blue representing the squares occupied by the different parts, and the black square denoting the square removed.