(fvco3d is a natural deduction form of fvco3 proved here:
https://github.com/metamath/set.mm/commit/454132a35254c17c4e54353b5c2c772eeb2ebb65#diff-12dc1484b058d1ee6cb68a74194d66c7R641421-R641429
)

-stan

On Sat, Mar 7, 2020 at 8:54 AM Stanislas Polu <[email protected]> wrote:

> Interesting!
>
> It basically comes from an attempt at satisfying the conditions
> for eliman0. Here's the full proof draft:
>
> ```
> $( <MM> <PROOF_ASST> THEOREM=imo72b2lem1  LOC_AFTER=?
>
> h1::imo72b2lem1.1      |- ( ph -> F : RR --> RR )
> h2::imo72b2lem1.7      |- ( ph -> E. x e. RR ( F ` x ) =/= 0 )
> h3::imo72b2lem0.6      |- ( ph -> A. y e. RR ( abs ` ( F ` y ) ) <_ 1 )
>
> !d84::        |- (  (  ph /\ x e. RR ) -> ( ( abs o. F ) ` x ) =/= (/) )
> d83:d84:adantrr       |- (  (  ph /\ ( x e. RR /\ ( F ` x ) =/= 0 ) ) -> (
> ( abs o. F ) ` x ) =/= (/) )
> d81:d83:neneqd     |- (  (  ph /\ ( x e. RR /\ ( F ` x ) =/= 0 ) ) -> -. (
> ( abs o. F ) ` x ) = (/) )
>
> d95:1:ffvelrnda     |- (  (  ph /\ x e. RR ) -> ( F ` x ) e. RR )
> d94:d95:adantrr    |- (  (  ph /\ ( x e. RR /\ ( F ` x ) =/= 0 ) ) -> ( F
> ` x ) e. RR )
> d92:d94:recnd         |- (  (  ph /\ ( x e. RR /\ ( F ` x ) =/= 0 ) ) -> (
> F ` x ) e. CC )
> d93::simprr        |- (  (  ph /\ ( x e. RR /\ ( F ` x ) =/= 0 ) ) -> ( F
> ` x ) =/= 0 )
> d91:d92,d93:absrpcld |- (  (  ph /\ ( x e. RR /\ ( F ` x ) =/= 0 ) ) -> (
> abs ` ( F ` x ) ) e. RR+ )
> d9:d91:rpgt0d      |- (  (  ph /\ ( x e. RR /\ ( F ` x ) =/= 0 ) ) -> 0 <
> ( abs ` ( F ` x ) ) )
>
> d80::simprl        |- (  (  ph /\ ( x e. RR /\ ( F ` x ) =/= 0 ) ) -> x e.
> RR )
> d82::eliman0       |- (  (  x e. RR /\ -. ( ( abs o. F ) ` x ) = (/) ) ->
> ( ( abs o. F ) ` x ) e. ( ( abs o. F ) " RR ) )
> d75:d80,d81,d82:syl2anc |- (  (  ph /\ ( x e. RR /\ ( F ` x ) =/= 0 ) ) ->
> ( ( abs o. F ) ` x ) e. ( ( abs o. F ) " RR ) )
> oeqaa::imaco |-  ( ( abs o. F ) " RR ) = ( abs " ( F " RR ) )
> d71:d75,oeqaa:syl6eleq |- (  (  ph /\ ( x e. RR /\ ( F ` x ) =/= 0 ) ) ->
> ( ( abs o. F ) ` x ) e. ( abs " ( F " RR ) ) )
> d73:1:adantr       |- (  (  ph /\ ( x e. RR /\ ( F ` x ) =/= 0 ) ) -> F :
> RR --> RR )
> d74::simprl        |- (  (  ph /\ ( x e. RR /\ ( F ` x ) =/= 0 ) ) -> x e.
> RR )
> d72:d73,d74:fvco3d |- (  (  ph /\ ( x e. RR /\ ( F ` x ) =/= 0 ) ) ->  ( (
> abs o. F ) ` x ) = ( abs ` ( F ` x ) ) )
> d7:d72,d71:eqeltrrd |- (  (  ph /\ ( x e. RR /\ ( F ` x ) =/= 0 ) ) -> (
> abs ` ( F ` x ) ) e. ( abs " ( F " RR ) ) )
>
> d10::simpr         |- (  (  (  ph /\ ( x e. RR /\ ( F ` x ) =/= 0 ) )  /\
> z = ( abs ` ( F ` x ) ) ) -> z = ( abs ` ( F ` x ) ) )
> d8:d10:breq2d      |- (  (  (  ph /\ ( x e. RR /\ ( F ` x ) =/= 0 ) ) /\ z
> =  ( abs ` ( F ` x ) ) ) -> ( 0 < z <-> 0 < ( abs ` ( F ` x ) ) ) )
>
> d6:d7,d8,d9:rspcedvd |- (  (  ph /\ ( x e. RR /\ ( F ` x ) =/= 0 ) ) -> E.
> z e. ( abs " ( F " RR ) ) 0 < z )
> qed:2,d6:rexlimddv  |- ( ph ->  E. z e. ( abs " ( F " RR ) ) 0 < z )
>
> $)
>
> -stan
>
> On Fri, Mar 6, 2020 at 11:58 PM Mario Carneiro <[email protected]> wrote:
>
>> The composition function value combination is easy enough to eliminate
>> using fvco, but the equality to the empty set is a type error, because the
>> lhs is a real number and the question of whether the empty set is a real
>> number is deliberately left ambiguous by the real number axioms. So I would
>> like to know what steps got you to this point. There are some function
>> value theorems that assume this as a "convenience" but there should be
>> analogues of them that don't (probably with some other assumption like the
>> function is a set).
>>
>> On Fri, Mar 6, 2020 at 8:02 AM 'Stanislas Polu' via Metamath <
>> [email protected]> wrote:
>>
>>> Thanks again Mario!
>>>
>>> I made more progress towards the final demonstration of the full IMO
>>> problem. Working on the following lemma:
>>>
>>> ```
>>> h1::imo72b2lem1.1      |- ( ph -> F : RR --> RR )
>>>
>>> h2::imo72b2lem1.7      |- ( ph -> E. x e. RR ( F ` x ) =/= 0 )
>>>
>>> h3::imo72b2lem0.6      |- ( ph -> A. y e. RR ( abs ` ( F ` y ) ) <_ 1 )
>>>
>>> ```
>>>
>>> I need to prove the following goal which seems pretty obvious but I'm
>>> struggling to find a way to discharge it:
>>>
>>> ```
>>> d84::        |- ( ( ph /\ x e. RR ) -> ( ( abs o. F ) ` x ) =/= (/) )
>>> ```
>>>
>>> Any idea on how to proceed with this?
>>>
>>> Thanks thanks!
>>>
>>> -stan
>>>
>>> On Thu, Mar 5, 2020 at 6:27 PM Mario Carneiro <[email protected]> wrote:
>>>
>>>> There is a theorem specifically for that translation, something like A.
>>>> x e. ( F " A ) P[x] <-> A. y e. A P[( F ` y )]. It's probably called ralima
>>>> but you've caught me on the bus again.
>>>>
>>>> Mario
>>>>
>>>> On Thu, Mar 5, 2020, 8:07 AM 'Stanislas Polu' via Metamath <
>>>> [email protected]> wrote:
>>>>
>>>>> Thanks Mario!
>>>>>
>>>>> I just finished formalizing the following lemma (which is a good chunk
>>>>> of the proof \o/):
>>>>>
>>>>> ```
>>>>>    $d F c x $. $d c ph x $.
>>>>>     imo72b2lem.1 $e |- ( ph -> F : RR --> RR ) $.
>>>>>     imo72b2lem.2 $e |- ( ph -> G : RR --> RR ) $.
>>>>>     imo72b2lem.3 $e |- ( ph -> A e. RR ) $.
>>>>>     imo72b2lem.4 $e |- ( ph -> B e. RR ) $.
>>>>>     imo72b2lem.5 $e |- ( ph -> ( ( F ` ( A + B ) ) + ( F ` ( A - B ) )
>>>>> ) = ( 2 x. ( ( F ` A ) x. ( G ` B ) ) ) ) $.
>>>>>     imo72b2lem.6 $e |- ( ph -> A. x e. ( abs " ( F " RR ) ) x <_ 1 ) $.
>>>>>     imo72b2lem.7 $e |- ( ph -> E. x e. RR ( F ` x ) =/= 0 ) $.
>>>>>
>>>>>     imo72b2lem $p |- ( ph -> ( ( abs ` ( F ` A ) ) x. ( abs ` ( G ` B
>>>>> ) ) ) <_ sup ( ( abs " ( F " RR ) ) , RR , < ) ) $=
>>>>> ```
>>>>>
>>>>> Proof here:
>>>>> https://github.com/spolu/set.mm/commit/454132a35254c17c4e54353b5c2c772eeb2ebb65
>>>>>
>>>>> One thing I'm quite dissatisfied with is the shape of `imo72b2lem.6`.
>>>>> I'd much rather have the more natural/intuitive expression `|- ( ph -> A. 
>>>>> x
>>>>> e. RR ( abs ` ( F `x ) ) <_ 1 )` but I completely failed to
>>>>> prove imo72b2lem.6 from it. Any help on this would be greatly appreciated!
>>>>>
>>>>> -stan
>>>>>
>>>>> On Wed, Mar 4, 2020 at 8:45 PM Mario Carneiro <[email protected]>
>>>>> wrote:
>>>>>
>>>>>> Can't look right now, but you should search for a theorem of the form
>>>>>> A = (/) <-> ( F " A ) = (/) .
>>>>>>
>>>>>> On Wed, Mar 4, 2020, 11:30 AM 'Stanislas Polu' via Metamath <
>>>>>> [email protected]> wrote:
>>>>>>
>>>>>>> I'm now looking to prove that `( abs " ( F " RR ) ) =/= (/)` given
>>>>>>> `F : RR --> RR`. From my exploration of the definition of --> I believe
>>>>>>> this should be enough but I don't see an easy path towards that? Would
>>>>>>> anybody have an example in mind that could give me a little bit of
>>>>>>> inspiration?
>>>>>>>
>>>>>>> Thanks for the continued support!
>>>>>>>
>>>>>>> -stan
>>>>>>>
>>>>>>> On Wed, Mar 4, 2020 at 6:29 PM Benoit <[email protected]>
>>>>>>> wrote:
>>>>>>>
>>>>>>>> Stan: you're right about the need to prove this (if using explicit
>>>>>>>> substitution): look for the utility theorems exchanging [. / ]. with 
>>>>>>>> other
>>>>>>>> symbols (quantifiers, operations).  As said by Jim and Thierry, who are
>>>>>>>> more experienced in proof building, implicit substitution might be 
>>>>>>>> easier
>>>>>>>> to use.  I think it is instructive to compare the details of both 
>>>>>>>> proving
>>>>>>>> styles on a specific example (e.g. ralbidv, suggested by Thierry, 
>>>>>>>> would be
>>>>>>>> analogous to exchanging [. / ]. with A.).
>>>>>>>>
>>>>>>>> Still, I think adding what I called rspesbcd could prove useful (if
>>>>>>>> it is not already in set.mm under another label; I cannot search
>>>>>>>> now, but it probably is already somewhere).
>>>>>>>>
>>>>>>>> BenoƮt
>>>>>>>>
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