ZSLECT returns .TRUE. if the eigenvalue Z is to be selected,
 otherwise it returns .FALSE.
 It is used by ZCHK41 to test if ZGEES successfully sorts eigenvalues,
 and by ZCHK43 to test if ZGEESX successfully sorts eigenvalues.
 The common block /SSLCT/ controls how eigenvalues are selected.
 If SELOPT = 0, then ZSLECT return .TRUE. when real(Z) is less than
 zero, and .FALSE. otherwise.
 If SELOPT is at least 1, ZSLECT returns SELVAL(SELOPT) and adds 1
 to SELOPT, cycling back to 1 at SELMAX.

Z

          Z is COMPLEX*16
          The eigenvalue Z.

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