Hi Mark,

>It's just that no-one's done it yet!

There are just two things that make proof assistants
difficult to use:

1. There is not sufficient automation of trivial stuff.

   I.e., you generally need to break down your reasoning into
   smaller steps than how you would experience things when
   you wouldn't be dealing with a proof assistant.  Maybe you
   _would_ experience those steps very fleetingly, but you
   wouldn't focus at them in the way a proof assistant
   forces you to.  It's like doing math veeeerrrrryyyy
   sllloooowwlllllyyy.

   If some step in a proof is obvious to you, you want to be
   able to just say "well, that's obvious" and nothing more.
   That's unfortunately not how it seems to work right now.
   Even if there's automation in a system that can solve
   such a problem, you need to be aware _what_ automation
   to invoke.

2. You need to be able to find things in a library, or
   establish that the thing you think you need is not
   there yet.

   And you need to be able to keep your library
   well-organised and in sync with the versions of your
   systems.  Not easy.

   Random example: suppose you want to use Schwarz's
   inequality in a proof.  So _here's_ your formalisation
   that you're working on, and _there's_ the library of your
   system.  Now what?  You will need to give search commands,
   or switch windows to look at lists of things you might
   need, or try to remember what the lemma was called and
   what was its exact shape... it's all irritating overhead.

   And when you prove something you will need to decide
   on a name for your new lemma.  That's something that's
   particularly difficult.

There are no other reasons proof assistants are difficult.
So will these be the two things you'll be addressing?

Of course these two things are related.  And Sledgehammer
clearly is trying to address these problems.  But yes,
it's not fully "done yet".

Freek

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