|   | Who Cites node? | 
 | 
| node | Def tree_node(<x, y>) == tree_node(<x,y>) | 
 | |   | Thm*  E:Type, x,y:Tree(E). tree_node(<x, y>)   Tree(E) | 
 | 
| tree_node | Def tree_node(x) == inr(x) | 
 | |   | Thm*  E,T:Type, x:(T T). tree_node(x)   tree_con(E;T) | 
 | |   | Thm*  E:Type, x,y:Tree(E). tree_node(<x,y>)   Tree(E) |