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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _det_tc(detector_name, ra, dec, tc, ref_frame='geocentric'):
 """Returns the coalescence time of a signal in the given detector. Parameters detector_name : string The name of the detector, e.g., 'H1'. ra : float The right ascension of the signal, in radians. dec : float The declination of the signal, in radians. tc : float The GPS time of the coalescence of the signal in the `ref_frame`. ref_frame : {'geocentric', string} The reference frame that the given coalescence time is defined in. May specify 'geocentric', or a detector name; default is 'geocentric'. Returns ------- float : The GPS time of the coalescence in detector `detector_name`. """

    if ref_frame == detector_name:
        return tc
    detector = Detector(detector_name)
    if ref_frame == 'geocentric':
        return tc + detector.time_delay_from_earth_center(ra, dec, tc)
    else:
        other = Detector(ref_frame)
        return tc + detector.time_delay_from_detector(other, ra, dec, tc)