SUBROUTINE SUSPEC( ierr )
C -----------------------------------------------------------------------------
C  Purpose: Add "spectator jet" (proton remnant) to LUJETS.
C
C    Notes: All produced spectator partons are assumed massless/virtual 
C           (even tops). 
C           The remnant is simulated by either e diquark with all the remaining
C           momentum of the proton, or a proton and a quark with half of this
C           momentum each.
C
C   Errors: >0 Skip an event
C
C   Author: JMB 
C   Last change 18/2/92 
C -----------------------------------------------------------------------------
C
      IMPLICIT NONE
C
      INCLUDE 'SUSANA.INC'
      INCLUDE 'PYTHIA57.INC'
C
      INTEGER ierr
C -   Reset error flag
      ierr = 0
C
C
C    Come here for electrons.
C
      IF (ISUSTR(8).EQ.0) THEN
      IF ( (ISUSTR(5).LE.3) 
     &     .AND. (outq_flav.GT.0.) ) THEN
C       Interacting parton was a u quark
        IF (isustr(3).EQ.1) THEN
          WRITE(isustr(1),*) 'suspec: An e- u event'
        ENDIF
        k(3,1) = 2
        k(3,2) = 2101
        p(3,1) = pp(1) * (1.0-xj)
        p(3,2) = pp(2) * (1.0-xj)
        p(3,3) = pp(3) * (1.0-xj)
        p(3,4) = pp(4) * (1.0-xj)
        IF ((-p(3,1)**2-p(3,2)**2-p(3,3)**2+p(3,4)**2).LT.0.0) THEN
          IF (isustr(3).GT.0) THEN
            WRITE(isustr(1),*) 'SUSPEC1:Neg.Sqrt:Skipping an event'
          ENDIF
          ierr = -1
          GOTO 8900
        ENDIF
        p(3,5) = SQRT(-p(3,1)**2-p(3,2)**2-p(3,3)**2+p(3,4)**2)
        n = 3
      ELSE
        k(3,1) = 2
        k(3,2) = 2212
        p(3,1) = pp(1) * (1.0-xj)/2.0
        p(3,2) = pp(2) * (1.0-xj)/2.0
        p(3,3) = pp(3) * (1.0-xj)/2.0
        p(3,4) = pp(4) * (1.0-xj)/2.0
        IF ((-p(3,1)**2-p(3,2)**2-p(3,3)**2+p(3,4)**2).LT.0.0) THEN
          IF (isustr(3).GE.0) THEN
            WRITE(isustr(1),*) 'SUSPEC2:Neg.Sqrt:Skipping an event'
          ENDIF
          ierr = -2
          GOTO 8900
        ENDIF
        p(3,5) = SQRT(-p(3,1)**2-p(3,2)**2-p(3,3)**2+p(3,4)**2)
        k(4,1) = 2
        IF ( (ISUSTR(5).LE.3).AND.(outq_flav.LT.0) )THEN
C         Interacting parton was a dbar quark
          k(4,2) =  1
          IF (isustr(3).EQ.1) THEN
            WRITE(isustr(1),*) 'SUSPEC: An e- dbar event'
          ENDIF
        ELSE IF ( (ISUSTR(5).LE.6).AND.(outq_flav.GT.0) )THEN
C         Interacting parton was a c quark
          k(4,2) = -4
          IF (isustr(3).EQ.1) THEN
            WRITE(isustr(1),*) 'SUSPEC: An e- c event'
          ENDIF
        ELSE IF ( (ISUSTR(5).LE.6).AND.(outq_flav.LT.0) )THEN
C         Interacting parton was an sbar quark
          k(4,2) =  3
          IF (isustr(3).EQ.1) THEN
            WRITE(isustr(1),*) 'SUSPEC: An e- sbar event'
          ENDIF
        ELSE IF ( (ISUSTR(5).LE.9).AND.(outq_flav.GT.0) )THEN
C         Interacting parton was a t quark
          k(4,2) = -6
          IF (isustr(3).EQ.1) THEN
            WRITE(isustr(1),*) 'SUSPEC: An e- t event'
          ENDIF
        ELSE IF ( (ISUSTR(5).LE.9).AND.(outq_flav.LT.0) )THEN
C         Interacting parton was a bbar quark
          k(4,2) =  5
          IF (isustr(3).EQ.1) THEN
            WRITE(isustr(1),*) 'suspec: An e- bbar event'
          ENDIF
        ENDIF
        p(4,1) = pp(1) * (1.0-xj)/2.0
        p(4,2) = pp(2) * (1.0-xj)/2.0
        p(4,3) = pp(3) * (1.0-xj)/2.0
        p(4,4) = pp(4) * (1.0-xj)/2.0
        IF ((-p(4,1)**2-p(4,2)**2-p(4,3)**2+p(4,4)**2).LT.0.0) THEN
          IF (isustr(3).GE.0) THEN
            WRITE(isustr(1),*) 'SUSPEC3:Neg.Sqrt:Skipping an event'
          ENDIF
          ierr = -3
          GOTO 8900
        ENDIF
        p(4,5) = SQRT(-p(4,1)**2-p(4,2)**2-p(4,3)**2+p(4,4)**2)
        n=4
      ENDIF
      ENDIF
C
C    Come here for positrons.
C
      IF (ISUSTR(8).EQ.1) THEN
      IF ( (ISUSTR(5).LE.3) 
     &     .AND. (outq_flav.GT.0.) ) THEN
C       Interacting parton was a d quark
        IF (isustr(3).EQ.1) THEN
          WRITE(isustr(1),*) 'suspec: An e+ d event'
        ENDIF
        k(3,1) = 1
        k(3,2) = 1103
        p(3,1) = pp(1) * (1.0-xj)
        p(3,2) = pp(2) * (1.0-xj)
        p(3,3) = pp(3) * (1.0-xj)
        p(3,4) = pp(4) * (1.0-xj)
        IF ((-p(3,1)**2-p(3,2)**2-p(3,3)**2+p(3,4)**2).LT.0.0) THEN
          IF (isustr(3).GT.0) THEN
            WRITE(isustr(1),*) 'SUSPEC1:Neg.Sqrt:Skipping an event'
          ENDIF
          ierr = -1
          GOTO 8900
        ENDIF
        p(3,5) = SQRT(-p(3,1)**2-p(3,2)**2-p(3,3)**2+p(3,4)**2)
        n = 3
      ELSE
        k(3,1) = 2
        k(3,2) = 2212
        p(3,1) = pp(1) * (1.0-xj)/2.0
        p(3,2) = pp(2) * (1.0-xj)/2.0
        p(3,3) = pp(3) * (1.0-xj)/2.0
        p(3,4) = pp(4) * (1.0-xj)/2.0
        IF ((-p(3,1)**2-p(3,2)**2-p(3,3)**2+p(3,4)**2).LT.0.0) THEN
          IF (isustr(3).GE.0) THEN
            WRITE(isustr(1),*) 'SUSPEC2:Neg.Sqrt:Skipping an event'
          ENDIF
          ierr = -2
          GOTO 8900
        ENDIF
        p(3,5) = SQRT(-p(3,1)**2-p(3,2)**2-p(3,3)**2+p(3,4)**2)
        k(4,1) = 2
        IF ( (ISUSTR(5).LE.3).AND.(outq_flav.LT.0) )THEN
C         Interacting parton was a ubar quark
          k(4,2) =  1
          IF (isustr(3).EQ.1) THEN
            WRITE(isustr(1),*) 'SUSPEC: An e+ubar event'
          ENDIF
        ELSE IF ( (ISUSTR(5).LE.6).AND.(outq_flav.GT.0) )THEN
C         Interacting parton was a s quark
          k(4,2) = -3
          IF (isustr(3).EQ.1) THEN
            WRITE(isustr(1),*) 'SUSPEC: An e+ c event'
          ENDIF
        ELSE IF ( (ISUSTR(5).LE.6).AND.(outq_flav.LT.0) )THEN
C         Interacting parton was an cbar quark
          k(4,2) =  4
          IF (isustr(3).EQ.1) THEN
            WRITE(isustr(1),*) 'SUSPEC: An e+ cbar event'
          ENDIF
        ELSE IF ( (ISUSTR(5).LE.9).AND.(outq_flav.GT.0) )THEN
C         Interacting parton was a b quark
          k(4,2) = -5
          IF (isustr(3).EQ.1) THEN
            WRITE(isustr(1),*) 'SUSPEC: An e+ t event'
          ENDIF
        ELSE IF ( (ISUSTR(5).LE.9).AND.(outq_flav.LT.0) )THEN
C         Interacting parton was a tbar quark
          k(4,2) =  6
          IF (isustr(3).EQ.1) THEN
            WRITE(isustr(1),*) 'suspec: An e+ tbar event'
          ENDIF
        ENDIF
        p(4,1) = pp(1) * (1.0-xj)/2.0
        p(4,2) = pp(2) * (1.0-xj)/2.0
        p(4,3) = pp(3) * (1.0-xj)/2.0
        p(4,4) = pp(4) * (1.0-xj)/2.0
        IF ((-p(4,1)**2-p(4,2)**2-p(4,3)**2+p(4,4)**2).LT.0.0) THEN
          IF (isustr(3).GE.0) THEN
            WRITE(isustr(1),*) 'SUSPEC3:Neg.Sqrt:Skipping an event'
          ENDIF
          ierr = -3
          GOTO 8900
        ENDIF
        p(4,5) = SQRT(-p(4,1)**2-p(4,2)**2-p(4,3)**2+p(4,4)**2)
        n=4
      ENDIF
      ENDIF
C
 8900 CONTINUE
      RETURN
      END