-DEFUN ("atan", Fatan, Satan, 1, 1, 0,
- "Return the inverse tangent of ARG.")
- (arg)
- register Lisp_Object arg;
+DEFUN ("atan", Fatan, Satan, 1, 2, 0,
+ doc: /* Return the inverse tangent of the arguments.
+If only one argument Y is given, return the inverse tangent of Y.
+If two arguments Y and X are given, return the inverse tangent of Y
+divided by X, i.e. the angle in radians between the vector (X, Y)
+and the x-axis. */)
+ (y, x)
+ register Lisp_Object y, x;