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

theorem
  A = B*^C+^D & D in C implies B = A div^ C & D = A mod^ C
proof
  assume that
A1: A = B*^C+^D and
A2: D in C;
  thus B = A div^ C by A1,A2,Def6;
  hence thesis by A1,Th52;
end;
