diff --git a/examples/math/Math.gf b/examples/math/Math.gf
index d5cbe9196..35cfcbfdc 100644
--- a/examples/math/Math.gf
+++ b/examples/math/Math.gf
@@ -21,6 +21,8 @@ fun
   LString : String -> Label ;
   VString : String -> Var ;
 
+  V_x, V_y, V_z : Var ; --- for js
+
   PLink : Proof ;
 
 -- lexicon
diff --git a/examples/math/MathEnz.gf b/examples/math/MathEnz.gf
index b362040c2..d30e8114b 100644
--- a/examples/math/MathEnz.gf
+++ b/examples/math/MathEnz.gf
@@ -27,6 +27,10 @@ lin
   LString s = s ;
   VString s = s ;
 
+  V_x = ss "x" ;
+  V_y = ss "y" ;
+  V_z = ss "z" ;
+
 -- lexicon
 
   Set  = ss "set" ;
diff --git a/examples/math/MathSwz.gf b/examples/math/MathSwz.gf
index 5e37d2f30..39fdd3374 100644
--- a/examples/math/MathSwz.gf
+++ b/examples/math/MathSwz.gf
@@ -27,6 +27,10 @@ lin
   LString s = s ;
   VString s = s ;
 
+  V_x = ss "x" ;
+  V_y = ss "y" ;
+  V_z = ss "z" ;
+
 -- lexicon
 
   Set  = ss "mängd" ;