In the beginning, there was only Addition.
Addition was made of a diagonal and a horizontal line.
They were best friends, those lines, and they loved each other dearly.
But one day Horizontal met someone else. Horizontal no longer wanted to be a part of Diagonal. He wanted to be with his new best friends, new lover. So he left.
Diagonal loved Horizontal, and she never stopped. He left a permanent mark on her, whereas Horizontal never found true love again.
And so Diagonal became Addition, with the mark of Horizontal forever engraved upon her, and Horizontal became Subtraction, all my himself.
*i just made this up, this is not realistic in any way