correct attribute projection for shared nodes

Example:

   ?- sat(A =:= B # C).
   %@ node(15): (v_i(A, 3)->node(13);node(14)),
   %@ node(14): (v_i(B, 4)->node(11);node(12)),
   %@ node(12): (v_i(C, 5)->false;true),
   %@ node(11): (v_i(C, 5)->true;false),
   %@ node(13): (v_i(B, 4)->node(12);node(11)).