code: func (m *abstractPagedMutable) Set(index, value int64) {
  	assert(index >= 0 && index < m.size)
  	pageIndex := m.pageIndex(index)
  	indexInPage := m.indexInPage(index)
  	m.subMutables[pageIndex].Set(indexInPage, value)
  }
docs: /* set value at index. */