function mode( S : SetOfKeys ) : SetOfKeys;
	var	A, A1, A2, A3 : SetOfKeys;
		Homog, Heter : set of SetOfKeys;
	begin
	Homog := [];
	Heter := [S];
	while LargestCardinality(Heter) > LargestCardinality(Homog) do
		begin
		A := LargestSet( Heter );
		med := median( A );
		split A into A1, A2, A3
			 { with elements <med; =med; >med  } 
		Heter := ( Heter - A ) + A1 + A3;
		Homog := Homog + A2
		end;
	LargestSet( Homog );
	end;