Hi, All very good questions. Here's my current thinking on the matter: `a` and `!a` are compatible types. The compiler will insert the `seq`s where needed. I don't think this is useless. First, it serves as good documentation. Documenting strictness properties, e.g. as we do in the container library today, is awkward. Strictness annotations on types would make the documentation precise and succinct. Second, it's a bit more declarative than having put manually put bang patterns at the right places in the function definition and having to remember (and teach beginners) how to do that correctly.. Third, it might help use generate better code, especially if we also implement Strict Core. I believe this is analogous to what Scala does for their by-value parameters, which types are preceded with a => annotation. Cheers, Johan