At: derive trans 1 1 2 2 2 1 1 1 1 1
1. V: Type
2. T: Type
3. G: Grammar(V;T)
4. l: (V+T)*
5. m: (V+T)*
6. n: (V+T)*
7. a1: ((V+T)*)*
8. ||a1|| > 0
9. l = a1[0]
10.
i:
(||a1||-1). a1[i] 
a1[(i+1)]
11. a1[(||a1||-1)] = m
12. a: ((V+T)*)*
13. ||a|| > 0
14. m = a[0]
15.
i:
(||a||-1). a[i] 
a[(i+1)]
16. a[(||a||-1)] = n
17. i:
(||firstn(||a1||-1;a1) @ a||-1)
18.
i < ||a1||-2
19. i > ||a1||-2
20. i+1-(||a1||-1) = i-(||a1||-1)+1
a[(i-(||a1||-1))] 
a[(i-(||a1||-1)+1)]
By: BackThru 15
Generated subgoals:None
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