prev isn't used atm

src/layout/layer.rs

@@ -7,7 +7,6 @@ use crate::{
 };
 
 struct LayerNode {
-    prev: Option<usize>,
     next: Next,
     child: Option<usize>,
     data: Layer,
@@ -57,7 +56,6 @@ impl Layers {
         }
         let i_next = self.push(LayerNode::new(Layer::default(), self.vec[i].next));
         self.vec[i].next = Next::Same(i_next);
-        self.vec[i_next].prev = Some(i);
         i_next
     }
 
@@ -67,7 +65,6 @@ impl Layers {
         }
         let i_next = self.push(LayerNode::new(Layer::default(), Next::Parent(i)));
         self.vec[i].child = Some(i_next);
-        self.vec[i_next].prev = Some(i);
         i_next
     }
 
@@ -116,7 +113,6 @@ impl IndexMut<usize> for Layers {
 impl LayerNode {
     pub fn new(data: Layer, next: Next) -> Self {
         Self {
-            prev: None,
             next,
             child: None,
             data,