ArcTan function

  DECLARATION:  ArcTan(x : Real);

      PURPOSE:  Returns the ArcTangent of the Argument.

         UNIT:  System

  RESULT TYPE:  Real

      REMARKS:  Where x is a Real-Type expression, the result is the
                principal value, in radians, of the arctangent of x.

      EXAMPLE:  Var
                   x : Real;

                Begin
                   x := ArcTan(Pi);
                End.