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 Th97:
  for t, u holds LD-EqClassOf (t => u) = (LD-EqClassOf t) => (LD-EqClassOf u)
proof
  let t, u;
  thus LD-EqClassOf (t => u)
      = (LD-EqClassOf t) '=' (LD-EqClassOf (t '&' u)) by Def93
      .= (LD-EqClassOf t) => (LD-EqClassOf u) by Def92;
end;
