anchor.diff:      else Zset.union s1 s2
   
   let emptyFreeTyvars =  
  -    { FreeTycons = emptyFreeTycons; 
  +    { FreeTycons = emptyFreeTycons
         /// The summary of values used as trait solutions
         FreeTraitSolutions = emptyFreeLocals
         FreeTypars = emptyFreeTypars}
  
positive.code: let accFreeLocalTycon opts x acc = 
      if not opts.includeLocalTycons then acc else
      if Zset.contains x acc.FreeTycons then acc else 
      {acc with FreeTycons = Zset.add x acc.FreeTycons } 
  
  let accFreeTycon opts (tcr:TyconRef) acc = 
      if not opts.includeLocalTycons then acc else
      match tcr.IsLocalRef with 
      | true -> accFreeLocalTycon opts tcr.PrivateTarget acc
      | _ -> acc
  
  let rec boundTypars opts tps acc = 
      // Bound type vars form a recursively-referential set due to constraints, e.g.  A : I<B>, B : I<A> 
      // So collect up free vars in all constraints first, then bind all variables 
      let acc = List.foldBack (fun (tp:Typar) acc -> accFreeInTyparConstraints opts tp.Constraints acc) tps acc
      List.foldBack (fun tp acc -> {acc with FreeTypars = Zset.remove tp acc.FreeTypars}) tps acc
  
  and accFreeInTyparConstraints opts cxs acc =
      List.foldBack (accFreeInTyparConstraint opts) cxs acc
  
negative.code: 
  and accFreeLocalValInTraitSln _opts v fvs =
      if Zset.contains v fvs.FreeTraitSolutions then fvs 
      else { fvs with FreeTraitSolutions = Zset.add v fvs.FreeTraitSolutions}
  
  and accFreeValRefInTraitSln opts (vref:ValRef) fvs = 
      if vref.IsLocalRef then
          accFreeLocalValInTraitSln opts vref.PrivateTarget fvs
      else
          // non-local values do not contain free variables 
          fvs
  
  and accFreeTyparRef opts (tp:Typar) acc = 
      if not opts.includeTypars then acc else
      if Zset.contains tp acc.FreeTypars then acc 
      else 
          accFreeInTyparConstraints opts tp.Constraints
            { acc with FreeTypars = Zset.add tp acc.FreeTypars}
  
  and accFreeInType opts ty acc  = 
      match stripTyparEqns ty with 
  