•Generation of topologies and insertion of fields

mesonstop = CreateTopologies[0, 2 -> 2, Adjacencies -> {4}, ExcludeTopologies -> {SelfEnergies, WFCorrections}, CountertermOrder -> 1] ;

mesontreeinsert = InsertFields[mesonstop, {Pion[0, {i1}], Pion[0, {i2}]} -> {Pion[0, {i3}], Pion[0, {i4}]}] ;

Converted by Mathematica  (July 10, 2003)