Physlib.QFT.PerturbationTheory.WickAlgebra.StaticWickTheorem

Let $\mathcal{F}$ be a field specification and $\phi_1, \phi_2, \dots, \phi_n$ be a list of field operators in $\mathcal{F}$. The static version of Wick's theorem states that the product of these operators in the Wick algebra is equal to the sum over all possible Wick contractions $\Lambda$ of the indices $\{0, 1, \dots, n-1\}$: $$\prod_{i=1}^n \phi_i = \sum_{\Lambda \in \text{WickContraction}(n)} \text{staticWickTerm}(\phi_1, \dots, \phi_n, \Lambda)$$ where a Wick contraction $\Lambda$ is defined as a collection of disjoint pairs of indices representing field pairings, and $\text{staticWickTerm}$ is the mathematical term in the Wick algebra resulting from the specific contraction $\Lambda$ applied to the sequence of field operators.