diff --git a/core/src/util.rs b/core/src/util.rs
index 5f3f7321..77d02735 100644
--- a/core/src/util.rs
+++ b/core/src/util.rs
@@ -56,4 +56,33 @@ impl<T> OptionEffect<T> for Option<T> {
         }
         self
     }
-}
\ No newline at end of file
+}
+
+#[derive(Clone, Debug, Eq, Hash, Ord, PartialOrd, PartialEq)]
+pub enum Either<L, R> {
+    Left(L),
+    Right(R),
+}
+
+// Cribbed from https://github.com/bluss/either/blob/f793721f3fdeb694f009e731b23a2858286bc0d6/src/lib.rs#L219-L259.
+impl<L, R> Either<L, R> {
+    pub fn map_left<F, M>(self, f: F) -> Either<M, R>
+        where F: FnOnce(L) -> M
+    {
+        use self::Either::*;
+        match self {
+            Left(l) => Left(f(l)),
+            Right(r) => Right(r),
+        }
+    }
+
+    pub fn map_right<F, S>(self, f: F) -> Either<L, S>
+        where F: FnOnce(R) -> S
+    {
+        use self::Either::*;
+        match self {
+            Left(l) => Left(l),
+            Right(r) => Right(f(r)),
+        }
+    }
+}
diff --git a/db/src/internal_types.rs b/db/src/internal_types.rs
index f97f1b0a..2955faf1 100644
--- a/db/src/internal_types.rs
+++ b/db/src/internal_types.rs
@@ -15,6 +15,8 @@
 use std::collections::HashMap;
 use std::rc::Rc;
 
+use mentat_core::util::Either;
+
 use errors;
 use errors::ErrorKind;
 use types::{
@@ -33,33 +35,6 @@ pub enum Term<E, V> {
     AddOrRetract(OpType, E, Entid, V),
 }
 
-#[derive(Clone, Debug, Eq, Hash, Ord, PartialOrd, PartialEq)]
-pub enum Either<L, R> {
-    Left(L),
-    Right(R),
-}
-
-// Cribbed from https://github.com/bluss/either/blob/f793721f3fdeb694f009e731b23a2858286bc0d6/src/lib.rs#L219-L259.
-impl<L, R> Either<L, R> {
-    pub fn map_left<F, M>(self, f: F) -> Either<M, R>
-        where F: FnOnce(L) -> M
-    {
-        match self {
-            Left(l) => Left(f(l)),
-            Right(r) => Right(r),
-        }
-    }
-
-    pub fn map_right<F, S>(self, f: F) -> Either<L, S>
-        where F: FnOnce(R) -> S
-    {
-        match self {
-            Left(l) => Left(l),
-            Right(r) => Right(f(r)),
-        }
-    }
-}
-
 use self::Either::*;
 
 /// An entid that's either already in the store, or newly allocated to a tempid.
diff --git a/db/src/tx.rs b/db/src/tx.rs
index 9ad0f496..50cb2c56 100644
--- a/db/src/tx.rs
+++ b/db/src/tx.rs
@@ -64,7 +64,6 @@ use edn::{
 use entids;
 use errors::{ErrorKind, Result};
 use internal_types::{
-    Either,
     KnownEntid,
     KnownEntidOr,
     LookupRef,
@@ -76,7 +75,10 @@ use internal_types::{
     TermWithTempIdsAndLookupRefs,
     TermWithoutTempIds,
     TypedValueOr,
-    replace_lookup_ref};
+    replace_lookup_ref,
+};
+
+use mentat_core::util::Either;
 
 use mentat_core::{
     DateTime,
diff --git a/db/src/upsert_resolution.rs b/db/src/upsert_resolution.rs
index 03cbf971..3c74562f 100644
--- a/db/src/upsert_resolution.rs
+++ b/db/src/upsert_resolution.rs
@@ -28,7 +28,9 @@ use internal_types::{
     TermWithoutTempIds,
     TermWithTempIds,
 };
-use internal_types::Either::*;
+
+use mentat_core::util::Either::*;
+
 use mentat_core::{
     attribute,
     Attribute,