[], literal(true) => head in Nodes;
[forall node in Nodes], !node.next=literal(0) => node.next in Nodes;
[forall node in Nodes], !node.next=literal(0) => <node, node.next> in nextnodes;
[forall node in Nodes], !node.prev=literal(0) => node.prev in Nodes;
[forall node in Nodes], !node.prev=literal(0) => <node, node.prev> in prevnodes;