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 Th16:
  a c= M or a in M implies M is Aleph
proof
  assume a c= M or a in M;
  then
A1: a c= M by ORDINAL1:16;
  omega c= a by Th15;
  then omega c= M by A1;
  hence thesis;
end;
