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