k:, f,g:(k), p:(k).
  sum(if p(i) f(i)+g(i) else f(i) fi | i < k)
  =
  sum(f(i) | i < k)+sum(if p(i) g(i) else 0 fi | i < k)

None

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