Diagonal lemma

Diagonal lemma is a type of theorem that talks about how two different numbers that can't be divided will fit together to make an even number. It's kind of like doing a jigsaw puzzle. Let's say you have 4 puzzle pieces. You can put them together to make a square that has 4 equal parts - that's the even number. But if you have 3 pieces and 2 pieces, it will not make a square; the pieces won't fit together. The Diagonal Lemma tells us that we can actually make two triangles from these pieces that will fit together perfectly. Then all of the pieces become part of one big number, and that number is even. So, the Diagonal Lemma helps us figure out how to fit these different numbers together to make something even.