some comments

transcript/src/basic.rs

@@ -32,6 +32,12 @@ impl<E: ExtensionField> Transcript<E> for BasicTranscript<E> {
     }
 
     fn read_challenge(&mut self) -> Challenge<E> {
+        // notice `from_bases` and `from_limbs` has the same behavior but 
+        // `from_bases` has a sanity check for length of input slices
+        // while `from_limbs` use the first two fields silently
+        // we select `from_base` here to make it being more clear that
+        // we only use the first 2 fields here to construct the 
+        // extension field (i.e. the challenge)
         let r = E::from_bases(&self.permutation.squeeze()[..2]);
 
         Challenge { elements: r }