IF YOU CAN SEE THIS go to http://www.cs.cornell.edu/Info/People/sfa/Nuprl/Shared/Xindentation_hack_doc.html
At:
member iff sublist T:Type, x:T, L:T List. (xL) [x] L
By:
Unfolds [`l_member`;`sublist`] 0 THEN Try (Unfold `label` 0 THEN Reduce 0)
THEN
All Reduce
THEN
ExRepD