  Reconstructing the evolution of post-common-envelope binaries (PCEBs) can
constrain current prescriptions of common-envelope (CE) evolution. Analyzing a
new sample of PCEBs we derive constraints on one of the most important
parameters in the field of close compact binary formation, i.e. the CE
efficiency alpha. After reconstructing the post-CE evolution and based on fits
to stellar evolution calculations as well as a parametrized energy equation for
CE evolution that incorporates realistic approximations of the binding energy
parameter lambda, we determine the possible evolutionary histories of the
observed PCEBs. We also reconstruct CE evolution replacing the classical energy
equation with a scaled angular momentum equation and compare the results
obtained with both algorithms. We find that all PCEBs in our sample can be
reconstructed with the energy equation if the internal energy of the envelope
is included. Although most individual systems have solutions for a broad range
of values for alpha, only for alpha=0.2-0.3 do we find simultaneous solutions
for all PCEBs in our sample. If we adjust alpha to this range of values, the
values of the angular momentum parameter gamma cluster in a small range of
values. In contrast if we fix gamma to a small range of values that allows us
to reconstruct all our systems, the possible ranges of values for alpha remains
broad for individual systems. The classical parametrized energy equation seems
to be an appropriate prescription of CE evolution and turns out to constrain
the outcome of the CE evolution much more than the alternative angular momentum
equation. If there is a universal value of the CE efficiency, it should be in
the range of alpha=0.2-0.3. We do not find any indications for a dependence of
alpha on the mass of the secondary star or the final orbital period.
