>
> How do I prove the last one in session 4: (A∨(A→⊥)→⊥)→⊥ ?
>>
>
> Heh... That one looks daunting for some reason. But fear not, search for 
> "Law of excluded middle implies double negation". Though, I was unable to 
> find a solution until I solved it myself with much swearing and sweating :(
>
Correcting myself from creating even more confusion: it should be actually 
vice versa - "Double negation elimination implies law of excluded middle". 

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