math library. Everything in Lua 5.1’s math is available too (math.abs, math.min, math.sin, …).
Lerp
Clamp
Round
Sign
Remap
NormalizeAngle
[-180, 180).
CalcAngle
QAngle pointing from one position to another.
GetFOV
0 through 180. view_angles is a QAngle, the other two are Vector.
AngleVectors
QAngle into three direction Vectors. Returns all three.
VectorAngles
Vector to a QAngle.