reserve phi,fi,psi for Ordinal-Sequence,
  A,A1,B,C,D for Ordinal,
  f,g for Function,
  X for set,
  x,y,z for object;
reserve f1,f2 for Ordinal-Sequence;
reserve W for Universe;
reserve A1,B1 for Ordinal of W,
  phi for Ordinal-Sequence of W;

theorem Th34:
  A1 in dom phi
proof
  dom phi = On W by FUNCT_2:def 1;
  hence thesis by ORDINAL1:def 9;
end;
