Fix a bug of using incorrect forest nodes to plant.

Previously some incorrect forest nodes will be used for planting new
nodes.  I cannot fix the root cause of their presence in the
chain-rule machine.  But I can ignore them when they are encountered.

Of course I would like to really prevent them from existing, but still
cannot figure out how.

1 files changed, 7 insertions, 2 deletions

diff --git a/chain/src/lib.rs b/chain/src/lib.rs
index bf3a8b4..f16ebb2 100644
--- a/chain/src/lib.rs
+++ b/chain/src/lib.rs
@@ -61,8 +61,13 @@ impl Edge {
         self.forest_source
     }
 
-    /// Return the associated bottom edge of the edge from which
-    /// onwards we shall perform the reduction.
+    /// Set the associated forest edge of the edge of the edge.
+    pub fn set_forest_source(&mut self, source: PaVi) {
+        self.forest_source = source;
+    }
+
+    /// Set the associated bottom edge of the edge from which onwards
+    /// we shall perform the reduction.
     pub fn set_true_source(&mut self, true_source: PaVi) {
         self.true_source = true_source;
     }