n(P(node-element-presence-none,=,a),P(node-element-presence-none,=,b),P(node-element-presence-none,=,c),P(node-element-presence-none,=,d)) P(node-element-presence-none,=,a) P(node-element-presence-none,=,b) P(node-element-presence-none,=,c) P(node-element-presence-none,=,d)