  In this work we present a number of generalizations of Wick's theorems on
integrals with Gaussian weight to a larger class of weights which we call
subgaussian. Examples of subgaussian contractions are that of Kac-Moody or
Virasoro type, although the concept of a subgaussian weight does not refer a
priori to two-dimensional field theory. The generalization was chosen in such a
way that the contraction rules become a combinatorical way of solving the
Schwinger-Dyson equation. In a still more general setting we prove a relation
between solutions of the Schwinger-Dyson equation and a map $N$, which in the
Gaussian case reduces to normal ordering. Furthermore, we give a number of
results concerning contractions of composite insertions, which do not suffer
from the Johnson-Low problem of ``commutation'' relations that do not satisfy
the Jacobi identity.
