  Recently Perlmutter et al. suggested a positive value of Einstein's
cosmological constant Lambda on the basis of luminosity distances from type-Ia
supernovae. However, Lambda world models had earlier been proposed by Hoell &
Priester and Liebscher et al. on the basis of quasar absorption-line data.
Employing more general repulsive fluids ("dark energy") encompassing the Lambda
component we quantitatively compare both approaches with each other.
  Fitting the SN-data by a minimum-component model consisting of dark energy +
dust yields a closed universe with a large amount of dust exceeding the
baryonic content constrained by big-bang nucleosynthesis. The nature of the
dark energy is hardly constrained. Only when enforcing a flat universe there is
a clear tendency to a dark-energy Lambda fluid and the `canonical' value
Omega_M = 0.3 for dust.
  Conversely, fitting the quasar-data by a minimum-component model yields a
sharply defined, slightly closed model with a low dust density ruling out
significant pressureless dark matter. The dark-energy component obtains an
equation-of-state P = -0.96 epsilon close to that of a Lambda-fluid. Omega_M =
0.3 or a precisely flat spatial geometry are inconsistent with
minimum-component models.
  It is found that quasar and supernova data sets cannot be reconciled with
each other via (repulsive ideal fluid+dust+radiation)-world models.
Compatibility could be reached by drastic expansion of the parameter space with
at least two exotic fluids added to dust and radiation as world constituents.
If considering such solutions as far-fetched one has to conclude that the
quasar absorption line and the SN-Ia constraints are incompatible.
