assert(s, 'failed to snapshot operation for undo history')
  assert(#State.lines > 0, 'failed to snapshot operation for undo history')
  assert(from.start_line == to.start_line, 'failed to patch undo operation')
  assert(#to.lines == to.end_line-to.start_line+1, 'failed to patch undo operation')
  assert(from.start_line == to.start_line, 'failed to patch undo operation')
  assert(#to.lines == to.end_line-to.start_line+1, 'failed to patch undo operation')
  for i=1,#to.lines do
    table.insert(line_cache, to.start_line+i-1, {})
  end
end
  for i=from.end_line,from.start_line,-1 do
    table.remove(line_cache, i)
  end
  for i=1,#to.lines do
    table.insert(lines, to.start_line+i-1, to.lines[i])
  end
end
  for i=from.end_line,from.start_line,-1 do
    table.remove(lines, i)
  end
  if s < 1 then s = 1 end
  if e == nil then

    assert(Text.le1(State.screen_top1, State.cursor1), ('screen_top (line=%d,pos=%d) is below cursor (line=%d,pos=%d)'):format(State.screen_top1.line, State.screen_top1.pos, State.cursor1.line, State.cursor1.pos))

  assert(minl < maxl, ('minl %d not < maxl %d'):format(minl, maxl))
  local rhs = State.lines[maxl].data:sub(max_offset)