function string:lstrip()
  if self == nil then
    return nil
    end
  local s = self:gsub("^%s+", "")
  return s
  end
function string:rstrip()
  if self == nil then
    return nil
    end
  local s = self:gsub("%s+$", "")
  return s
  end
function string:strip()
  return self:lstrip():rstrip()
  end
