| Description: Define the class of
cosets by 𝑅: 𝑥 and 𝑦 are cosets by
𝑅 iff there exists a set 𝑢 such
that both 𝑢𝑅𝑥 and
𝑢𝑅𝑦 hold, i.e., both 𝑥 and
𝑦
are are elements of the 𝑅
-coset of 𝑢 (see dfcoss2 39120 and the comment of dfec2 8696). 𝑅 is
usually a relation.
This concept simplifies theorems relating partition and equivalence: the
left side of these theorems relate to 𝑅, the right side relate to
≀ 𝑅 (see e.g. pet 39582).
Without the definition of ≀ 𝑅 we
should have to relate the right side of these theorems to a composition
of a converse (cf. dfcoss3 39121) or to the range of a range Cartesian
product of classes (cf. dfcoss4 39122), which would make the theorems
complicated and confusing. Alternate definition is dfcoss2 39120.
Technically, we can define it via composition (dfcoss3 39121) or as the
range of a range Cartesian product (dfcoss4 39122), but neither of these
definitions reveal directly how the cosets by 𝑅 relate to each
other. We define functions (df-funsALTV 39383, df-funALTV 39384) and
disjoints (dfdisjs 39410, dfdisjs2 39411, df-disjALTV 39407, dfdisjALTV2 39416)
with the help of it as well. (Contributed by Peter Mazsa,
9-Jan-2018.) |
