IF YOU CAN SEE THIS go to /sfa/Nuprl/Shared/Xindentation_hack_doc.html
At:
permute sum12 1. n : 2. (n-1) List
3. u : (n-1)
4. v : (n-1) List
5. f:(n). sum(f(compose_flips(v)(x)) | x < n) = sum(f(x) | x < n)
f:(n). sum(f(compose_flips([u / v])(x)) | x < n) = sum(f(x) | x < n)
By:
Assert (f:(n). sum((f o compose_flips(v))(x) | x < n) = sum(f(x) | x < n))