code: func unionBitmapArrayInPlace(a, b *Container) {
  	a.unmapBitmap()
  	bitmap := a.bitmap()
  	for _, v := range b.array() {
  		bitmap[v>>6] |= (uint64(1) << (v % 64))
  	}
  }
docs: // unions array b into bitmap a, mutating a in place. The n value
  // of a will need to be repaired after the fact.