def group_repr(group_keys):
    """Get a string representation of a list of group keys"""
    if len(group_keys) == 0:
        return "{}"
    elif len(group_keys) == 1:
        return str(group_keys[0])
    else:
        out = f"{group_keys[0]}"
        for key in group_keys[1:]:
            out += " x "
            out += key
        return out