def assume_in_vitro_based_enzyme_modification_assertions(ac):
    """ write a JTMS assumption specifying that in vitro-based evidence is acceptable

    @param ac:bool True if action is to assert!, False if action is to
                 retract!, None to get the representation of the assumption
    @returns: a string representation of the appropriate JTMS
    assumption
    """
    rep = "(accept-in-vitro-based-enzyme-modulation-assertions)"
    
    if ac == True:
        return "(assume! '%s 'dikb-inference-assumption)" % rep
    elif ac == False:
        return "(retract! '%s 'dikb-inference-assumption)" % rep
    else:
        return rep