toplevel "OR";
"OR" or "A" "B";
"A" wsp "AND" "C";
"B" wsp "C" "R" "S";
"C" wsp "Q" "R";
"AND" and "P" "Q";
"P" lambda=0.1 dorm=0.9;
"Q" lambda=0.2 dorm=0.8;
"R" lambda=0.3 dorm=0.7;
"S" lambda=0.4 dorm=0.6;