1. Covering of a set S. A finite set of subsets of S whose union is just S
itself. The subsets, A1, A2..... Am
are said to cover S. If the elements A1 for i = 1, 2.....m
are mutually disjoint, then the
is called a partition of S.
2. A relationship between two elements of a partially ordered set
S. If x and y are elements of S then y covers x if and only if x<y,
and whenever x≤z≤y for some
element z in S, then either x = z or z = y.