This can happen: when you use nodelta.

diff --git a/matita/components/ng_tactics/nCicTacReduction.ml b/matita/components/ng_tactics/nCicTacReduction.ml
index c1eba801fad00960f5d1a1fe76abe4f40106ca0c..96a795c3472e8c4ee1a767edd92bc133af331b82 100644 (file)
--- a/matita/components/ng_tactics/nCicTacReduction.ml
+++ b/matita/components/ng_tactics/nCicTacReduction.ml
@@ -15,7 +15,6 @@ let rec normalize status ?(delta=0) ~subst ctx t =
  normalize_machine status ~delta ~subst ctx
   (fst (NCicReduction.reduce_machine status ~delta ~subst ctx (0,[],t,[])))
 and normalize_machine status ?(delta=0) ~subst ctx (k,e,t,s) =
- assert (delta=0);
  let t = 
    if k = 0 then t
    else