def range_overlap(a, b):
    """
    >>> range_overlap(("1", 30, 45), ("1", 45, 55))
    True
    >>> range_overlap(("1", 30, 45), ("1", 57, 68))
    False
    >>> range_overlap(("1", 30, 45), ("2", 42, 55))
    False
    """
    a_chr, a_min, a_max = a
    b_chr, b_min, b_max = b
    # must be on the same chromosome
    if a_chr!=b_chr: return False 
    return (a_min <= b_max) and (b_min <= a_max)