T Generator
   F.virtual.abstract next() -> Float

T PowersGenerator(Generator)
   i = 0.0
   Float e

   F (e)
      .e = e

   F.virtual.assign next() -> Float
      V r = .i ^ .e
      .i++
      R r

T Filter
   Generator gen, filter
   Float lastG, lastF

   F (Generator gen, filter)
      .gen = gen
      .filter = filter
      .lastG = .gen.next()
      .lastF = .filter.next()

   F ()()
      L .lastG >= .lastF
         I .lastG == .lastF
            .lastG = .gen.next()
         .lastF = .filter.next()

      V out = .lastG
      .lastG = .gen.next()
      R out

V gen = Filter(PowersGenerator(2), PowersGenerator(3))

L 20
   gen()
L 10
   print(gen(), end' ‘ ’)