[Ur] need help with unification and field name disjointness proof failures

[Adam Chlipala]

On 04/06/2017 04:52 PM, Benjamin Barenblat wrote:
> In addition, on your first TODO (‘use better crypto functions’), you
> may be interested in my cryptographic random¹ and hash² libraries. I’d
> be thrilled to incorporate patches for the latter if you want to add
> more OpenSSL hash functions (PBKDF2 in particular would be extremely
> welcome and probably quite applicable to your current work).
>
> ¹ https://benjamin.barenblat.name/git/urweb-crypto-random-openssl.git
> ² https://benjamin.barenblat.name/git/urweb-crypto-hash-openssl.git

I thought Ur/Web's built-in [rand] function was already 
cryptographically secure.  Did I get something wrong there?