CURVE /PERIODIC

        [GREG1\]CURVE /PERIODIC

    Specifies that the curve is periodic (and  currently  closed  also).  If
    /VARIABLE X,   it   expects  that  y(1)=y(NXY) ;  if  /VARIABLE Y,  that
    x(1)=x(NXY) ; and in the case of a parametric  curve,  that  x(1)=x(NXY)
    and y(1)=y(NXY).