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uct of some contribution from G c and some one from Λ. If the contribution of G c is of n$_{1}$ order of perturbation theory and of Λ of n$_{2}$ order when the order of 〈 U ( β ) 〉 c 0 is equal to n with the condition n$_{1}$ + n$_{2}$ + 2 = n which must be satisfied. There are different possibilities to sat- 

isfy this condition and all of them must be taken into account. 

For example there are three possibilities to compose from G c and Λ the sixth diagrams of Fig. 7. These pos- sibilities are enumerated below on the Fig. 8. Other ex- 

