fx
fy
xf xfx xfy
yf yfx

----------------------------------------------------

[
	["builtin", "fx"],
	["builtin", "fy"],
	["builtin", "xf"], ["builtin", "xfx"], ["builtin", "xfy"],
	["builtin", "yf"], ["builtin", "yfx"]
]

----------------------------------------------------

Checks for builtins.