A new generalized Wick theorem for interacting fields in 2D conformal field
theory is described. We briefly discuss its relation to the Borcherds identity
and its derivation by an analytic method. Examples of the calculations of the
operator product expansions by using the generalized Wick theorems including
fermionic fields are also presented.Comment: 12 pages, to appear in the Proceedings of the International Workshop
"CQIS-2016" (St. Petersburg, Russia