fix typo

shashi · shashi · commit 388691a3fc85 · 2021-01-08T08:45:59.000-05:00
diff --git a/src/utils.jl b/src/utils.jl
@@ -309,7 +309,7 @@ xˍtt(t)
 ```
 """
 function diff2term(O)
-    istree(O)) || return O
+    istree(O) || return O
     if is_derivative(O)
         (x, t, order) = flatten_differential(O)
         return lower_varname(x, t, order)
