def get_amr_line(input_f):
    """
    Read the file containing AMRs. AMRs are separated by a blank line.
    Each call of get_amr_line() returns the next available AMR (in one-line form).
    Note: this function does not verify if the AMR is valid

    """
    cur_amr = []
    has_content = False
    for line in input_f:
        line = line.strip()
        if line == "":
            if not has_content:
                # empty lines before current AMR
                continue
            else:
                # end of current AMR
                break
        if line.strip().startswith("#"):
            # ignore the comment line (starting with "#") in the AMR file
            continue
        else:
            has_content = True
            cur_amr.append(line.strip())
    return "".join(cur_amr)