def METHOD_NAME(self, i: int) -> bool:
    """True if lines[i:i+1] form an underlined line."""
    lines = self.lines
    if i + 1 < len(lines):
        line0 = lines[i]
        line1 = lines[i + 1]
        ch0 = self.is_underline(line0)
        ch1 = self.is_underline(line1)
        return not ch0 and not line0.isspace() and ch1 and len(line1) >= 4
    return False