toplevel "A";
"A" and "B" "B'";
"B" and "C" "D" "PDEP";
"B'" and "C'" "D'" "PDEP'";
"PDEP" pdep=0.6 "B" "C";
"PDEP'" pdep=0.6 "B'" "C'";
"C" lambda=0.5 dorm=0;
"D" lambda=0.5 dorm=0;
"C'" lambda=0.5 dorm=0;
"D'" lambda=0.5 dorm=0;