radarctan
RADARCTAN num
(RADARCTAN x y)
outputs the arctangent, in radians, of its input. With two
inputs, outputs the arctangent of y/x, if x is nonzero, or
pi/2 or -pi/2 depending on the sign of y, if x is zero.
The expression 2*(RADARCTAN 0 1) can be used to get the
value of pi.