def generate_dot_nn(start=['x', 'y'],lsizes=[4,4,4], end=['out']):
  prefixes = 'abcdefg'
  layers = []
  layers.append(start)
  for e, i in enumerate(lsizes):
    layers.append(["%s%d" % (prefixes[e], j) for j in range(i)])
  layers.append(end)
  for i in range(1, len(layers)):
    str = ""
    for ii in layers[i-1]:
      for jj in layers[i]:
        str += "%s->%s;" % (ii, jj)
    print(str)

generate_dot_nn()