Nuprl - Proof: select concat 2 1 2 1 1 2 1 1

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At: select concat 2 1 2 1 1 2 1 1

1. T : Type
2. (T List) List
3. u : T List
4. v : (T List) List
5.

||concat(v)||.
5.

||v||.
5. ||concat(firstn(m;v))||

n
5. & n-||concat(firstn(m;v))||<||v[m]||
5. & concat(v)[n] = v[m][(n-||concat(firstn(m;v))||)]
6. n :

||u @ concat(v)||
7.

n<||u||
8. m :

||v||
9. ||concat(firstn(m;v))||

n-||u||
10. n-||u||-||concat(firstn(m;v))||<||v[m]||
11. concat(v)[(n-||u||)] = v[m][(n-||u||-||concat(firstn(m;v))||)]

n-||u @ concat(firstn(m;v))||<||[u / v][(m+1)]||

By:	Subst ([u / v][(m+1)] ~ v[m]) 0

Generated subgoals:

1 [u / v][(m+1)] ~ v[m]
1 step

2 n-||u @ concat(firstn(m;v))||<||v[m]||
1 step

About:

IF YOU CAN SEE THIS go to /sfa/Nuprl/Shared/Xindentation_hack_doc.html

1	[u / v][(m+1)] ~ v[m]	1 step
2	n-\|\|u @ concat(firstn(m;v))\|\|<\|\|v[m]\|\|	1 step