Shevuot 2: Two That Are Four

A new - and long - mishnah: Those who violate their oaths need to bring a sacrifice for not following through on their commitment (2 such cases). But is that only with regard to the future (with the past, another 2 are added)? Likewise, 2 that are 4 with regard to the oaths of the kohanim. Plus, 2 that are 4 in carrying from on domain to another (that is, from private to public; and then public to private is added to make 4). Plus, the various stages of lack of awareness while on is transgressing -- which can have impact on the person's sin-offerings. With various opinions represented in the mishnah (including that of Rabbi Shimon and Rabbi Meir - regarding the cases of the lack of awareness).