theorem Th26:
  S is Sub_atomic implies ((@S`1).1)`1 <> 0 & ((@S`1).1)`1 <> 1 &
  ((@S`1).1)`1 <> 2 & ((@S`1).1)`1 <> 3
proof
  assume S is Sub_atomic;
  then ex k being Nat st (@S`1).1 is QC-pred_symbol of k,A by Th25;
  hence thesis by QC_LANG1:17;
end;
