diff --git a/stl/robustness.py b/stl/robustness.py
index c9475c0..14963ba 100644
--- a/stl/robustness.py
+++ b/stl/robustness.py
@@ -66,5 +66,7 @@ def eval_terms(lineq, x, t):
 
 
 def eval_term(x, t):
-    # TODO(lift interpolation much higher)
-    return lambda term: term.coeff*np.interp(t, x.index, x[term.id.name])
+    def _eval_term(term):
+        coeff = float(term.coeff) if term.coeff.is_number else term.coeff
+        return coeff*np.interp(t, x.index, x[term.id.name])
+    return _eval_term
diff --git a/stl/utils.py b/stl/utils.py
index 6f169c9..5f7b185 100644
--- a/stl/utils.py
+++ b/stl/utils.py
@@ -33,7 +33,9 @@ def type_pred(*args:List[Type]) -> Mapping[Type, bool]:
 def _child_lens(psi:STL, focus:Lens) -> STL_Generator:
     if psi is None:
         return
-    if isinstance(psi, NaryOpSTL):
+    elif psi is stl.TOP or psi is stl.BOT:
+        return
+    elif isinstance(psi, NaryOpSTL):
         for j, _ in enumerate(psi.args):
             yield focus.args[j]
     else: