reserve x for set,
  i for Instruction of SCM+FSA,
  a,b for Int-Location,
  f for FinSeq-Location,
  l, l1 for Nat,
  s,s1,s2 for State of SCM+FSA,
  P,P1,P2 for Instruction-Sequence of SCM+FSA;

theorem
  UsedI*Loc swap(a, b) = {}
proof
  set i0 = FirstNotUsed Macro (a := b) := a;
  set i1 = a := b;
  set i2 = b := FirstNotUsed Macro (a := b);
  thus UsedI*Loc swap(a, b) = (UsedI*Loc (i0 ";" i1)) \/ (UsedInt*Loc i2)
  by SF_MASTR:46
    .= (UsedI*Loc (i0 ";" i1)) \/ {} by SF_MASTR:32
    .= (UsedInt*Loc i0) \/ (UsedInt*Loc i1) by SF_MASTR:47
    .= (UsedInt*Loc i0) \/ {} by SF_MASTR:32
    .= {} by SF_MASTR:32;
end;
