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Abstract We review the technique of calculation of operator expansion coefficients. The main emphasis is put on gluon operators which appear in expansion of n ‐point functions induced by colourless quark currents. Two convenient schemes are discussed in detail: the abstract operator method and the method based on the Fock‐Schwinger gauge for the vacuum gluon field. We consider a large number of instructive examples important from the point of view of physical applications.
Novikov et al. (Sun,) studied this question.