Page "Schwinger function" Paragraph 0

In quantum field theory, the Wightman distributions can be analytically continued to analytic functions in Euclidean space with the domain restricted to the ordered set of points in Euclidean space with no coinciding points.

These functions are called the Schwinger functions, named after Julian Schwinger, and they are analytic, symmetric under the permutation of arguments ( antisymmetric for fermionic fields ), Euclidean covariant and satisfy a property known as reflection positivity.