from collections import defaultdict


def convert_tab_to_dict(response):
    """Convert tab response to dictionary.\n
    Response is a string made of rows with two tab separated columns."""

    if not type(response) == type("hola"):
        print("The argument is not a string.")
        return {}
    result = defaultdict(set)
    for entry in response.splitlines()[1:]:
        from_id, to_id = tuple(entry.split())
        result[from_id].add(to_id)
    return result