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)