Concept of ordered set

Any set S with a relation, say less than equal(<=) to is said to be ordered if for any two elements X and Y of S, either X<= Y or Y <= X is true. Then we may also say (S, <=) is an ordered set.

We know given two integer, say N1 and N2, we can always say whether N1<=N2 and N2 <=N1. Similarly if you are given two rational numbers or the real numbers, say N1 and N2, then it is always possible to tell whether N1 <= N2 or N2 <= N1.

Pattern of ordered set: An ordered set of numbers or objects; the order helps you predict what will come next, because this order follow a pattern unit to generate a set/list. 

Pattern unit: The part of a pattern that repeats.