SUBROUTINE  KONNC

C     [NEXT, CONSTANT]
C     SELECT P3 TO DEFINE THE NEXT TRIANGLE ALONG A CONSTANT CONTOUR.
C     POINTS P1 AND P2 OF THE NEW TRIANGLE WILL BE POINTS OF THE OLD
C     TRIANGLE, WHILE P3 WILL BE A NEW POINT GOTTEN BY REFLECTION OF
C     THE MISSING POINT IN THE OPPOSITE EDGE.
C     [24-MAY-73]

      COMMON/KON/ M1(2),M2(2),M3(2),Z1,Z2,Z3

      IF (SIGN(1.0,Z1).EQ.SIGN(1.0,Z3)) GO TO 10
      I=M1(1)-M2(1)+M3(1)
      J=M1(2)-M2(2)+M3(2)
      CALL KONXV (2,3)
      M3(1)=I
      M3(2)=J
      RETURN

   10 IF (SIGN(1.0,Z2).EQ.SIGN(1.0,Z3)) RETURN
      I=-M1(1)+M2(1)+M3(1)
      J=-M1(2)+M2(2)+M3(2)
      CALL KONXV (1,3)
      M3(1)=I
      M3(2)=J
      RETURN

      END