Chain

A chain C is a subset of a partial order subset P which is linearly ordered.

Example:

Let P = {1, 2, 3, 4, 4.5, 5, 5.8, 6}, and (P, ≤) is a partial order, where ≤ stands for the usual order of natural numbers.

Then: A = {1, 2, 3}, B = {1, 2, 4, 5, 6} are chains.