reserve k,m,n for Element of NAT,
  i, j for Nat,
  a, b, c for object,
  X, Y, Z for set,
  D, D1, D2 for non empty set;
reserve p, q, r, s for FinSequence;
reserve t, u, v, w for GRZ-formula;
reserve R, R1, R2 for GRZ-rule;
reserve A, A1, A2 for non empty Subset of GRZ-formula-set;
reserve B, B1, B2 for Subset of GRZ-formula-set;
reserve P, P1, P2 for GRZ-formula-sequence;
reserve S, S1, S2 for GRZ-formula-finset;
reserve x, y, z for LD-EqClass;

theorem Th96:
  for t, u holds LD-EqClassOf (t 'or' u)
      = (LD-EqClassOf t) 'or' (LD-EqClassOf u)
proof
  let t, u;
  thus LD-EqClassOf (t 'or' u)
      = 'not' LD-EqClassOf (('not' t) '&' ('not' u)) by Def91
      .= 'not' ((LD-EqClassOf 'not' t) '&' (LD-EqClassOf 'not' u)) by Def92
      .= 'not' (('not' LD-EqClassOf t) '&' (LD-EqClassOf 'not' u)) by Def91
      .= (LD-EqClassOf t) 'or' (LD-EqClassOf u) by Def91;
end;
