toplevel "A";
"A" and "B" "C";
"B" or "BE1" "BE2";
"C" and "BE3" "D";
"D" or "BE1" "BE4";
"BE1" lambda=0.5 dorm=0.3;
"BE2" lambda=0.5 dorm=0.3;
"BE3" lambda=0.5 dorm=0.3;
"BE4" lambda=0.5 dorm=0.3;