reserve i,j for Nat;
reserve i,j for Nat,
  x for variable,
  l for quasi-loci;
reserve C for initialized ConstructorSignature,
  c for constructor OperSymbol of C;

theorem Th29:
  [rng l, i] in Vars & l^<*[rng l,i]*> is quasi-loci
  proof
    varcl rng l = rng l by ABCMIZ_1:33;
    hence [rng l, i] in Vars by ABCMIZ_1:17; then
    reconsider x = [rng l, i] as variable;
    rng l in {rng l, i} & {rng l, i} in x by TARSKI:def 2; then
    vars x = rng l & x nin rng l by XREGULAR:7;
    hence thesis by ABCMIZ_1:31;
  end;
