IF YOU CAN SEE THIS go to http://www.cs.cornell.edu/Info/People/sfa/Nuprl/Shared/Xindentation_hack_doc.html
At:
no repeats iff T:Type, l:T List. no_repeats(T;l) (x,y:T. x before ylx = y)
By:
Unfolds [`no_repeats`;`l_before`] 0 THEN Unfold `sublist` 0
1. T : Type
2. l : T List
3. i,j:. i<||l|| j<||l|| i = jl[i] = l[j]
4. x : T 5. y : T 6. f:(||[x; y]||||l||).
6. increasing(f;||[x; y]||) & (j:||[x; y]||. [x; y][j] = l[(f(j))])
x = y