diff --git a/src/util/_impl/_sort_impl.scad b/src/util/_impl/_sort_impl.scad
index f95905db..051922b6 100644
--- a/src/util/_impl/_sort_impl.scad
+++ b/src/util/_impl/_sort_impl.scad
@@ -1,11 +1,4 @@
-function _greaterThan(elem1, elem2, i) =
-    i == -1              ? false :
-    elem1[i] > elem2[i]  ? true :
-    elem1[i] == elem2[i] ? _greaterThan(elem1, elem2, i - 1) : false;
-    
-function greaterThan(elem1, elem2) = _greaterThan(elem1, elem2, len(elem1));
-    
-function lessThan(elem1, elem2) = !greaterThan(elem1, elem2) && elem1 != elem2;
+use <util/_impl/_vt_default_comparator.scad>;
 
 function _default_sort(lt) = 
     let(leng = len(lt))
diff --git a/src/util/_impl/_vt_default_comparator.scad b/src/util/_impl/_vt_default_comparator.scad
new file mode 100644
index 00000000..1ab484a9
--- /dev/null
+++ b/src/util/_impl/_vt_default_comparator.scad
@@ -0,0 +1,8 @@
+function _greaterThan(elem1, elem2, i) =
+    i == -1              ? false :
+    elem1[i] > elem2[i]  ? true :
+    elem1[i] == elem2[i] ? _greaterThan(elem1, elem2, i - 1) : false;
+    
+function greaterThan(elem1, elem2) = _greaterThan(elem1, elem2, len(elem1));
+    
+function lessThan(elem1, elem2) = !greaterThan(elem1, elem2) && elem1 != elem2;
\ No newline at end of file
diff --git a/src/util/bsearch.scad b/src/util/bsearch.scad
index 4098d219..68c0f436 100644
--- a/src/util/bsearch.scad
+++ b/src/util/bsearch.scad
@@ -1,11 +1,4 @@
-function _greaterThan(elem1, elem2, i) =
-    i == -1              ? false :
-    elem1[i] > elem2[i]  ? true :
-    elem1[i] == elem2[i] ? _greaterThan(elem1, elem2, i - 1) : false;
-    
-function greaterThan(elem1, elem2) = _greaterThan(elem1, elem2, len(elem1));
-    
-function lessThan(elem1, elem2) = !greaterThan(elem1, elem2) && elem1 != elem2;
+use <util/_impl/_vt_default_comparator.scad>;
 
 function _binary_search(sorted, elem, low, upper) =
     low > upper ? -1 :
@@ -13,4 +6,5 @@ function _binary_search(sorted, elem, low, upper) =
     lessThan(sorted[mid], elem) ? _binary_search(sorted, elem, mid + 1, upper) :
     greaterThan(sorted[mid], elem) ? _binary_search(sorted, elem, low, mid - 1) : mid;
 
+// for example, `sorted` is by zyx
 function bsearch(sorted, elem) = _binary_search(sorted, elem, 0, len(sorted) - 1);
\ No newline at end of file