[en] In this contribution, the problem of criticality for neutron transport equation is studied. It is assumed that the medium considered is moving in general while its temperature, density and velocity are part-by part continuous functions of the space variables. Next it is supposed that effective cross-sections of neutron scattering, absorption and of fission are either real functions or distributions of neutron velocity and of medium temperature and velocity. At first the problem without a feedback is analyzed. In condition that the temperature, density and velocity of the medium are known functions, the task is transformed to the dominant eigenvalue problem of linear operator in suitably chosen linear space of complex functions. The existence of positive solution to this problem and also its uniqueness are proved. Then the results obtained are employed to analysis of the case when the medium temperature, density and velocity feedback is considered i.e. when the quantities just mentioned are bound with each other and with solution φ to the problem of criticality. The task is transformed to non-linear eigenproblem in normalized cone of nonnegative functions and it is shown: For any positive number q, the non-linear eigenproblem has nontrivial solution λ=λ_(q) >0 and φ=φ_(q) such that the norm of φ_(q) equals q. It is proved also that under certain conditions there exists critical state (i.e. λ =1). Finally some applications of the results obtained are shown and possible difficulties concerning the construction of the solution to the criticality problem with a feedback are pointed out. (author)