reserve fi,psi for Ordinal-Sequence,
  A,A1,B,C,D for Ordinal,
  X,Y for set,
  x,y for object;

theorem Th38:
  A in B+^C implies A in B or ex D st D in C & A = B+^D
proof
  assume that
A1: A in B+^C and
A2: not A in B;
  consider D such that
A3: A = B+^D by A2,Th27,ORDINAL1:16;
  take D;
  assume not thesis;
  then C c= D by A3,ORDINAL1:16;
  hence contradiction by A1,A3,ORDINAL1:5,ORDINAL2:33;
end;
