Renormalized operator form of quantum action principle

The derivatives of the renormalized field operator with respect to the parameters (coupling constants, masses) are discussed. Two ways of obtaining the finite result in terms of renormalized perturbation expansion are shown. Throughout the paper the operator language is used; in particular the operator formula for renormalized powers of the field operators (normal products) is employed. The λ?⁴ theory is considered as an illustrative example.