reserve k,n,m for Nat,
  A,B,C for Ordinal,
  X for set,
  x,y,z for object;
reserve f,g,h,fx for Function,
  K,M,N for Cardinal,
  phi,psi for
  Ordinal-Sequence;
reserve a,b for Aleph;

theorem Th15:
  a <> 0 & a <> 1 & a <> 2 & a <> card n & card n in a & omega c= a
proof
  omega c= a & card n in omega by CARD_3:85;
  hence thesis;
end;
