In the framework of the functional integral approach the bi-local composite fields were introduced to describe the Cooper pairs in superconducting many - fermion systems. In the special class of functions depending only on the difference of the coordinates of two fermions the composite fields are the superconducting order parameters. The effective action of the bi-local composite fields was established. From the variational principle for this effective action it follows the quantum equations of the composite fields. As the consequences the equations for the superconducting order parameters were derived. The pairing was considered in both spin states of two fermions: the singlet and triplet states. Discussions were presented on the applications of the functional integral techniques to some related problems: spontaneous magnetization and method to study its coexistence with the superconductivity, method to study the superconductivity in the strongly correlated fermion systems.
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