diff --git a/src/lib.rs b/src/lib.rs
index 42d9e67..3af0741 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -6,6 +6,7 @@
 /// position, index, or key to a hashmap. It should allow O(1) access to the Node.
 pub trait GraphLike<Node, NodeId> {
     fn get_node(&self, id: NodeId) -> Option<&Node>;
+    fn set_node(&mut self, id: NodeId, node: Node);
     fn iter_ids(&self) -> impl Iterator<Item = NodeId>;
     fn iter_neighbor_ids(&self, id: NodeId) -> impl Iterator<Item = NodeId>;
 
@@ -21,23 +22,26 @@ pub trait GraphLike<Node, NodeId> {
 
     /// TODO: Replace return type with a result that explains the reason for failure. This could
     /// help with rollback to recover from impossible generation
-    fn collapse_one(&mut self, rules: &impl Ruleset<Node, NodeId>) -> Option<NodeId> where NodeId: Copy, Self: Sized {
+    fn single_step(&mut self, rules: &impl Ruleset<Node, NodeId>) -> Option<NodeId> where NodeId: Copy, Self: Sized {
         let id = rules.find_lowest_entropy(self)?;
-        rules.choose(self, id);
+        let node = rules.choose(self, id).expect("Ruleset::choose should also return Some if Ruleset::entropy returns Some");
+        let empty_ids = self.iter_empty();
+        
         None
     }
 }
 
 pub trait Ruleset<Node, NodeId> {
     fn entropy(&self, graph: &impl GraphLike<Node, NodeId>, id: NodeId) -> Option<f32> where NodeId: Copy;
-    fn choose(&self, graph: &impl GraphLike<Node, NodeId>, id: NodeId) -> Node where NodeId: Copy;
+    fn choose(&self, graph: &impl GraphLike<Node, NodeId>, id: NodeId) -> Option<Node> where NodeId: Copy;
 
     fn find_lowest_entropy(&self, graph: &impl GraphLike<Node, NodeId>) -> Option<NodeId> where NodeId: Copy {
         graph.iter_empty()
             .map(|id| (id, self.entropy(graph, id)))
-            // Option<f32> apparently implements PartialOrd
+            // NOTE: Option<f32> implements PartialOrd
             // None is considered smaller than any Some value
             // This works out, since we want to find impossible nodes (entropy returns None)
+            // But make sure this doesn't cause unexpected behavior later on
             .min_by(|a, b| a.1.partial_cmp(&b.1).unwrap())
             .map(|(id, _)| id)
     }