diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -29,7 +29,7 @@
 
 ```bash
 cabal update
-cabal install --overwrite-policy=always phino-0.0.0.61
+cabal install --overwrite-policy=always phino-0.0.0.62
 phino --version
 ```
 
diff --git a/phino.cabal b/phino.cabal
--- a/phino.cabal
+++ b/phino.cabal
@@ -1,6 +1,6 @@
 cabal-version: 3.0
 name: phino
-version: 0.0.0.62
+version: 0.0.0.63
 license: MIT
 synopsis: Command-Line Manipulator of 𝜑-Calculus Expressions
 description: Please see the README on GitHub at <https://github.com/objectionary/phino#readme>
diff --git a/src/Render.hs b/src/Render.hs
--- a/src/Render.hs
+++ b/src/Render.hs
@@ -216,7 +216,7 @@
 
 instance Render NUMBER where
   render INDEX{..} = printf "\\indexof{ %s }" (render attr)
-  render LENGTH{..} = printf "|%s|" (render binding)
+  render LENGTH{..} = printf "\\vert %s \\vert" (render binding)
   render LITERAL{..} = show num
 
 instance Render COMPARABLE where
diff --git a/test/CLISpec.hs b/test/CLISpec.hs
--- a/test/CLISpec.hs
+++ b/test/CLISpec.hs
@@ -843,7 +843,7 @@
             , "\\trrule{ALPHA}"
             , "  { [[ B_1, \\tau_1 -> ?, B_2 ]] ( \\tau_2 -> e ) }"
             , "  { [[ B_1, \\tau_1 -> ?, B_2 ]] ( \\tau_1 -> e ) }"
-            , "  { if $ \\indexof{ \\tau_2 } = |B_1| $ }"
+            , "  { if $ \\indexof{ \\tau_2 } = \\vert B_1 \\vert $ }"
             , "  { }"
             , "\\trrule{COPY}"
             , "  { [[ B_1, \\tau -> ?, B_2 ]] ( \\tau -> e_1 ) }"