Niddah

R. Samuel citing R. Johanan ruled: If a woman has a settled period, her husband  may  calculate the days of that period and  come in unto her.  Said R. Samuel b. Yeba to R. Abba: Did R. Johanan refer also to a young wife who  is too shy to perform immersion? — The other replied: Did then R. Johanan speak of one who had actually  observed a discharge? It may [in fact be held] that R. Johanan spoke  only of a case where it is doubtful whether or not the woman did observe a discharge and where, [so that] even if some reason could be found for assuming that she did observe one, it may also be assumed that she had since performed immersions,  but in a case where it is certain that she had observed a discharge, who could say that she had since performed immersion? And, seeing that it is a question of a doubt  being opposed by a certainty  [she must be deemed unclean] since a doubt cannot take one out of a certainty. But does it not? Was it not in fact taught: If a haber  died and left a store-room full of fruits, even if they were only then due to be tithed,  they are presumed to have been properly prepared.  Now here it is a case of certain tebel  and there is only the doubt as to whether or not it was tithed, and the doubt nevertheless sets aside the certainty? — No, there it is a case of a certainty against a certainty, in agreement with a statement of R. Hanina of Hozae,  for R. Hanina of Hozae said: It is presumed with a haber that he does not allow anything to pass out of his control unless it has been duly prepared. And if you prefer I might say: It is a case of doubt against doubt, since [the man might have acted] in accordance with a suggestion of R. Oshaia, for R. Oshaia said: A man  may resort to a device with his produce and store it  together with its chaff  so that  his cattle may eat of it  and it is exempt from the tithe. But does not a doubt set aside a certainty? Surely it has been taught: It once happened that the handmaid of a certain tax-collector in Rimmon  threw the body of a premature child into a pit, and a priest  came and gazed into it to ascertain whether it was male or female,  and when the matter came before the Sages  they pronounced him clean because weasels and martens are commonly found there.  Now here, surely, it is a certainty that the woman had thrown a premature child into the pit and a doubt whether they had dragged it away or not, and yet does not the doubt set aside the certainty? — Do not read, 'Threw the body of a premature child into a pit' but