The diagrams that are formed by linking the half-lines in the X s with the external half-lines, representing insertions, are the Feynman diagrams of this theory. Each line carries a factor of ⁠ 1 / k ⁠, the propagator, and either goes from vertex to vertex, or ends at an insertion. If it is internal, it is integrated over. At each vertex, the total incoming k is equal to the total outgoing k.