  The concentration compactness framework for semilinear elliptic equations
without compactness, set originally by P.-L.Lions for constrained minimization
in the case of homogeneous nonlinearity, is extended here to the case of
general nonlinearities in the standard mountain pass setting of
Ambrosetti-Rabinowitz. In these setting, existence of solutions at the mountain
pass level is verified under a single penalty condition analogous to that in
the Lions' case. Problems on the whole space and problems with critical
nonlinearity are considered. Particular attention is given to nonhomogeneous
critical nonlinearities that oscillate about the "critical stem".
