Build-a-function Game

This game or whatever this is is simple. Whoever comes up with the best function for a named custom function based on the name gets to choose the next custom function and provide some parameters for others to solve. Functions which give no output and/or do not perform the stated rule don't count. I'll start.

SPHITTRI SP%, X1%, Y1%, X2%, Y2%, X3%, Y3%
'Detects collision between a sprite and a triangle.

You want us to make a function for you and others?

You want us to make a function for you and others?

that's not the point of this game (at least not the original point)

You want us to make a function for you and others?

Sure if you want to put it that way. It can be a learning thing a fun thing or a random thing based around custom functional functions. I'm just curious to see if something like this would work and how much people would challenge each other.