Rav holds that one who swears about someone else having done something in the past would be a valid oath as it can be formulated in the negative (and disagrees with Shmuel who holds that it can’t since it can’t be formulated in the future tense). Abaye points out that if it were someone saying he/she knows testimony and doesn’t, since it the negative it would be an “oath of testimony” and not an “oath of expression,” one would not be obligated. This leads to a whole discussion regarding why the Torah specified an “oath of testimony” if it could have been included in an “oath of expression.” Rabbi Yishmael and Rabbi Akiva debate their opinions (which cases are included in an oath of expression for which one needs to bring a sliding scale sin offering) based on how each one extrapolates the verses using different exegetical principles. An oath of expression is only brought if the person is “shogeg” – accidental but not if they did it on purpose or if it was totally beyond one’s control. The gemara tries to find a case where it could be accidental relating to a past event that wouldn’t be considered totally beyond one’s control. An oath of expression is only brought by one who “forgot” the oath but not the object. What is the case?