Niddah

'Rabbi stated: R. Judah b. Agra's ruling  is acceptable where she did not examine'. Now  what is meant by 'she did not examine'? If it be suggested that she examined herself in the twilight of R. Judah but did not examine herself in the twilight of R. Jose [the difficulty would arise]: From this  it follows that R. Judah holds  that even where she examined herself both times,  the possibility of zibah must be considered; [but why should this be so] seeing that she did examine herself?  It is obvious then [that the meaning  is] that she did not examine herself either in the twilight of R. Judah or in that of R. Jose;  but if she had examined herself in R. Judah's twilight  and did not examine herself in R. Jose's  there is no need for her to consider the possibility [of zibah].  It is thus clear that the twilight of R. Jose is according to Rabbi  regarded as night.  Now read the final clause: 'And the ruling of the Sages where she did examine' — What is meant by 'she did examine'? If it be suggested that she examined herself in the twilight of R. Judah but did not examine herself in that of R. Jose,  it would follow  that the Rabbis are of the opinion that even if she did not examine herself in either  there is no need to consider the possibility of zibah [but why should this be so] seeing that she did not examine herself?  It is obvious then that [the meaning  is] that she examined herself both in the twilight of R. Judah and in that of R. Jose, but that if she had examined herself in the twilight of R. Judah and not in that of R. Jose the possibility of zibah  must be considered.  It is thus clear that the twilight of R. Jose is according to Rabbi  regarded as doubtful time.  Does not this then present a contradiction between two statements of Rabbi?  — It is this that he  meant: The view of R. Judah b. Agra  is acceptable to the Rabbis  when she did not examine herself at all either in R. Judah's twilight or in that of R. Jose's, for even the Sages differed from him  only when she has examined herself in R. Judah's twilight  and did not examine herself in that of R. Jose,  but where she did not examine herself at all they agree with him,  But does not the following show incongruity?  [For it was taught:] If a woman observed a bloodstain, the observation being one of a large one,  she must take into consideration the possibility of a discharge at twilight,  but if the observation was one of a small stain  she should not take the possibility into consideration. This is the ruling of R. Judah b. Agra who cited it in the name of R. Jose. Said Rabbi: I heard from him  that in both cases must the possibility be taken into consideration; 'and', he said to me, 'it is for this reason: What if she had been a menstruant who did not  make sure of her cleanness  from the minha time  and onwards, would she not  have been regarded as being in a presumptive state of uncleanness?  And his ruling is acceptable to me where she has examined herself. Now what is meant by 'she has examined herself'? If it be suggested that she has examined herself in the twilight of R. Judah and did not examine herself in that of R. Jose, it would follow that R. Judah b. Agra holds that even though she did not examine herself either in the twilight of R. Judah or in that of R. Jose the possibility need not be considered; but why should this be so seeing that she did not examine herself? It must be obvious then that she did examine herself both in the twilight of R. Judah and in that of R. Jose. Thus it follows that R. Judah b. Agra holds that if she examined herself in the twilight of R. Judah and not in that of R. Jose she need not consider the possibility. It is thus clear that the twilight of R. Jose is according to R. Judah b. Agra regarded as night. Does not this then present a contradiction between two rulings of R. Judah b. Agra?  In the absence of Rabbi's interpretations  there would well be no difficulty, since the former ruling might refer to a case where she has examined herself in R. Judah's twilight and not in that of R. Jose while here it is a case where she has examined herself in R. Jose's twilight as in that of R. Judah's; but with Rabbi's interpretations  does not the contradiction arise? — Two Tannas expressed different views as to the opinion of R. Judah b. Agra. The first Tanna holds that the twilight of R. Judah ends first