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diff --git a/Dragon/src/SYB4TN.f b/Dragon/src/SYB4TN.f
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+*DECK SYB4TN
+      SUBROUTINE SYB4TN (NHMAX,IXRAYO,ISDEBU,COSECT,NRI,RAYONS,DELTAC)
+*
+*-----------------------------------------------------------------------
+*
+*Purpose:
+* Search of the next singular point in a Cartesian cell.
+*
+*Copyright:
+* Copyright (C) 2002 Ecole Polytechnique de Montreal
+* This library is free software; you can redistribute it and/or
+* modify it under the terms of the GNU Lesser General Public
+* License as published by the Free Software Foundation; either
+* version 2.1 of the License, or (at your option) any later version
+*
+*Author(s): A. Hebert
+*
+*Parameters: input
+* NHMAX   number of intervals (the number of interceptions is NHMAX+1).
+* IXRAYO  tubes indices from west to east.
+* ISDEBU  index of the first sector.
+* COSECT  cosinus of the sector angles.
+* NRI     number of radius.
+* RAYONS  radius of the tubes.
+*
+*Parameters: input/output
+* DELTAC  next distance.
+*
+*-----------------------------------------------------------------------
+*
+*----
+*  SUBROUTINE ARGUMENTS
+*----
+      INTEGER        NHMAX,IXRAYO(NHMAX),ISDEBU,NRI
+      REAL           COSECT(*),RAYONS(NRI),DELTAC
+*----
+*  LOCAL VARIABLES
+*----
+      LOGICAL        LGSEC1,LGSEC2
+*
+      IF (NHMAX .LT. 2) RETURN
+      IHX = 0
+      IR1 = IXRAYO(1)
+      IR2 = IXRAYO(2)
+      LGSEC2 = IR1 .EQ. IR2
+      IF (LGSEC2) THEN
+        ISC = ISDEBU + 1
+      ELSE
+        ISC = ISDEBU
+      ENDIF
+*
+      DO IHC = 2, NHMAX - 1
+        LGSEC1 = LGSEC2
+        IR0 = IR1
+        IR1 = IR2
+*
+        IR2 = IXRAYO(IHC+1)
+        LGSEC2 = IR1 .EQ. IR2
+        IF (LGSEC2) THEN
+          ISC = ISC + 1
+        ENDIF
+*
+* Tangente = Intersection Couronne
+        IF (IR2 .EQ. IR0) THEN
+        IF (IR2 .EQ. IR1+1) THEN
+          IF (RAYONS(IR1) .LT. DELTAC) THEN
+            DELTAC = RAYONS(IR1)
+            IHX = IHC
+          ENDIF
+        ENDIF
+*
+* Coin Secteur/Rayon
+        ELSEIF (LGSEC1) THEN
+        IF (IR2 .EQ. IR1+1) THEN
+          RR  = RAYONS(IR1)
+          DD  = RR * COSECT(ISC-1)
+          IF (DD .LT. DELTAC) THEN
+            DELTAC = DD
+            IHX = IHC
+          ENDIF
+        ENDIF
+*
+* Coin Secteur/Rayon
+        ELSEIF (LGSEC2) THEN
+        IF (IR0 .EQ. IR1+1) THEN
+          RR  = RAYONS(IR1)
+          DD  = RR * COSECT(ISC-1)
+          IF (DD .LT. DELTAC) THEN
+            DELTAC = DD
+            IHX = IHC
+          ENDIF
+        ENDIF
+*
+        ENDIF
+*
+      ENDDO
+*
+      RETURN
+      END