-(* the delift function takes in input an ordered list of integers [n1,...,nk]
- and a term t, and relocates rel(nk) to k. Typically, the list of integers
- is a parameter of a metavariable occurrence. *)
+(* the delift function takes in input an ordered list of optional terms *)
+(* [t1,...,tn] and a term t, and substitutes every tk = Some (rel(nk)) with *)
+(* rel(k). Typically, the list of optional terms is the explicit substitution *)(* that is applied to a metavariable occurrence and the result of the delift *)
+(* function is a term the implicit variable can be substituted with to make *)
+(* the term [t] unifiable with the metavariable occurrence. *)
+(* In general, the problem is undecidable if we consider equivalence in place *)
+(* of alpha convertibility. Our implementation, though, is even weaker than *)
+(* alpha convertibility, since it replace the term [tk] if and only if [tk] *)
+(* is a Rel (missing all the other cases). Does this matter in practice? *)