diff --git a/src/flow/traversible.rs b/src/flow/traversible.rs
index f23818d..81a371c 100644
--- a/src/flow/traversible.rs
+++ b/src/flow/traversible.rs
@@ -1,7 +1,6 @@
 //! Traversible binary trees.
 
 pub mod algorithms;
-pub mod unbalanced;
 
 use std::rc::Rc;
 
diff --git a/src/lib.rs b/src/lib.rs
index faaf441..2dfc989 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -3,6 +3,7 @@
 
 pub mod flow;
 pub mod func;
+pub mod mrds;
 pub mod rcore;
 pub mod rstd;
 #[cfg(test)]
diff --git a/src/mrds.rs b/src/mrds.rs
new file mode 100644
index 0000000..a68d2d5
--- /dev/null
+++ b/src/mrds.rs
@@ -0,0 +1,7 @@
+//! # Memory-resident data strucures
+//! Provided as examples of implementing [`flow`] traits.
+
+#[cfg(doc)]
+use crate::flow;
+
+pub mod trees;
diff --git a/src/mrds/trees.rs b/src/mrds/trees.rs
new file mode 100644
index 0000000..4eb74ad
--- /dev/null
+++ b/src/mrds/trees.rs
@@ -0,0 +1 @@
+pub mod unbalanced;
diff --git a/src/flow/traversible/unbalanced.rs b/src/mrds/trees/unbalanced.rs
similarity index 98%
rename from src/flow/traversible/unbalanced.rs
rename to src/mrds/trees/unbalanced.rs
index 917690e..513f988 100644
--- a/src/flow/traversible/unbalanced.rs
+++ b/src/mrds/trees/unbalanced.rs
@@ -2,12 +2,11 @@
 //!
 //! Intended for testing.
 
-use std::fmt::Display;
+use std::{fmt::Display, rc::*};
 
+use crate::flow::traversible::*;
 use crate::func::*;
 
-use super::*;
-
 pub struct UnbalancedData;
 
 impl PartialEq for UnbalancedData {
@@ -172,7 +171,7 @@ impl<'a, T: Monad<'a>, A: 'a> UnbalancedConstructor<'a, T, A> {
 mod tests {
     use rand::{Rng, SeedableRng};
 
-    use crate::rstd::tracing::*;
+    use crate::{flow::comparator::*, rstd::tracing::*};
 
     use super::{algorithms::contains::*, algorithms::subset::*, *};