At: nd ext valcom 1 1 2 2 2 1 2 2
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)
2of(hd(rev([ < p,nil > ]))) = nil 
Alph*
By:
RecUnfold `reverse` 0
THEN
Reduce 0
Generated subgoals:None
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