BeginPackage["deltasimplify`"]

(*
  deltasimplify.m
    This package defines objects and procedures to carry out spin sums.
    
    Programmer:  Dick Furnstahl furnstahl.1@osu.edu
    
    Revision history:
      09-Feb-2003  --- original version
      
*)

Unprotect["deltasimplify`*"]
Clear["deltasimplify`*"]

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DeltaSimplify::usage = "DeltaSimplify[e] simplifies a spin sum"

del::usage = "del[a,b] is a Kronecker delta function with indices a,b."

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Begin["`Private`"]

deltasimprules = {
  x_ (del[a_,b_]+y_) :> x*del[a,b] + x*y,
  del[a_,b_]*del[b_,c_] :> del[a,c],
  del[a_,b_]*del[c_,b_] :> del[a,c],
  del[a_,b_]*del[a_,c_] :> del[b,c],
  del[a_,b_]*del[c_,a_] :> del[b,c],
  del[a_,b_]*del[a_,b_] :> del[a,a], 
  del[a_,b_]*del[b_,a_] :> del[a,a], 
  del[a_,a_] :> -Global`g
}


DeltaSimplify[e_] := FixedPoint[ Expand[# //. deltasimprules]&, e]

End[(* "`Private`" *)]

(***********************************************************************)

Protect["deltasimplify`*"]

EndPackage[]