#!/usr/bin/env ruby

def eqon(a,b)
  (yield a) == (yield b)
end

s = ARGF.read

def section start; /#{start}.+?(?=(?:#{start}|\z))/m; end
def line start;   /^#{start}.+/; end
def lines start; /(?:#{line start}\n)+/m; end
hunks = section /^diff/
hunk = section /^@@[^\n]*@@/
minus = lines /-/
plus = lines /\+/
minusplus = /(?:#{minus }|#{plus})+/m

s.gsub!(hunks) { |hs|
  r = hs.gsub(hunk) { |h|
    h.scan(minusplus).reject { |c|
      eqon(minus, plus) { |r|
        c.scan(r).map{ |l|
          l.gsub(/^./,"").gsub(/\s+/m,"")
        }
      }
    }.empty? ? "" : h
    # }.empty? ? h : "" # uncomment this to see what nitpicking would get removed
  }

  r.scan(hunk).empty? ? "" : r
}

puts s