reserve T, X, Y for Subset of MC-wff;
reserve p, q, r, s for Element of MC-wff;
reserve T, X, Y for Subset of MC-wff;
reserve p, q, r for Element of MC-wff;
reserve T, X, Y for Subset of MC-wff;
reserve p, q, r for Element of MC-wff;

theorem Th86:
  (Nes p) => Nes (Nes p) in CnS4 (X)
proof
  T is S4_theory & X c= T implies (Nes p) => Nes (Nes p) in T;
  hence thesis by Def23;
end;
