I have previously heard about the mathematics operation Rubble. I think it's fabricated, and I want to get this confirmed.
Rubble have the symbol $h$, but backwards. It works as addition, times two.
Examples:
$1h1\Rightarrow 2\Rightarrow 4$
$50h50\Rightarrow 100\Rightarrow 200$
A complete shot in the dark, but the Hamburglar was a character in oldish McDonald's commercials. He said "rubble rubble" a lot. Kind of sounds like "double double."
And the operator is an $h$.
Maybe the term was the fabrication of a fairly cool math professor who ate a lot of Happy Meals?