At: nd ext valcom 1 1 2 1 1 1 1 1 1 2 2 1 1 2 1
1. Alph: Type
2. St: Type
3. NDA: NDA(Alph;St)
4. C: (St
Alph*)*
5. ||C|| > 0
6. 
i:
(||C||-1). ||2of(C[i])|| > 0
7. q: St
8. a: Alph
9. p: St
10. NDA(C)
q
11. 
NDA(q,a,p)
12. i: 
13. 0
i
14. i < ||map(
c. < 1of(c),a.2of(c) > ;C)||+1-1
15. 
i < ||C||-1
16. i+1-||map(c. < 1of(c),a.2of(c) > ;C)|| = 0 
1
17. z: 1
2of(hd(nth_tl(z;[ < p,nil > ]))) Alph*
By: RecCaseSplit `nth_tl`
Generated subgoals:None
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