So then here's a smaller lemma: for all x and all q:
If(not(x))
Then provable(if x then q): by definition of if-then
So replace x by Provable(P) and q by p.
Where's the flaw?
The flaw is that you are correctly noticing that provable(if(not(x) then (if x then q)), and incorrectly concluding if(not(x)) then provable(if x then q). It is true that if(not(x)) then (if x then q), but if(not(x)) is not necessarily provable, so (if x then q) is also not necessarily provable.
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