On 3/03/12 12:29 AM, Wishnu Prasetya wrote:
> Hey guys,
> 
> When playing with HOL recently I had a problem in rewriting a set 
> comprehension. BETA_CONV refuses to reduce this:
> 
>      --`{x | x >0}  x`--
> 
> I use pred_set, so that should be the same as --`(\x. x>0) x`--.
> 
> Bug or feature?

Even when using pred_set, the term

  { x | x > 0 }

is not syntactically equal to (\x. x > 0).

Rather it is equal to

  GSPEC (\x. (x, x > 0))

The simplifier will automatically handle terms such as

  ``y IN {x | x > 0}``

and you should definitely avoid getting into the situation where you
have a set comprehension applied to an argument (as above).

I hope this helps.

Michael


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