CS-2OAKs.
A CS-2OAK (2OAK stands for two of a kind) is any two of the same number anywhere in the FSN as long as the two numbers are not grouped.

CS-Pairs.
A CS-Pair is two of the same number that are grouped anywhere in the FSN.

CS-Two Pairs.
A CS-Two Pair is a CS-Pair of one number and a CS-Pair of another number appearing anywhere in the FSN, and the two identical numbers must be grouped together and do not need to be grouped with the other CS-Pair: M xx2299xx M or M 22xxxx99 M.

CS-Random Two Pairs.
A CS-Random Two Pairs is a CS-2OAK of one number and a CS-2OAK of another number appearing anywhere in the FSN. The numbers can be totally randomized in the FSN, or one CS-Pair can be grouped, but not both CS-Pairs. At least one CS-Pair must be separated: M xx229x9x M or M 2x9x2xx9 M.

CS-Tri Pairs.
CS-Tri Pairs are three sets of CS-Pairs appearing anywhere in the FSN, and the CS-Pairs do not need to be grouped with the other CS-Pairs: M 112233xxx M or M x22x3311 M.

CS-Random Tri Pairs.
CS-Tri Pairs are three sets of CS-2OAKs randomly appearing anywhere in the FSN: M 12313x2xx M or M 1x232x31 M. Two CS-Pairs may be grouped but not all three M 12233xx1 M.

CS-Quad Pairs.
CS-Quad Pairs contain four sets of CS-Pairs appearing in sequence anywhere in the FSN. All CS-Pairs must be grouped with its other number with no separations between the similar numbers: M 11223344 M or M 22443311 M.

CS-Random Quad Pairs.
CS-Random Quad Pairs are four CS-Pairs anywhere in the FSN. The CS-Pairs do not need to be grouped, but at least one CS-Pair must be separated from its twin. In other words, a CS-2OAK: M 12432314 M or M 44123231 M.

S-Pairs in Pairs.
C With CS-Pairs in Pairs, a CS-Pair must be within a CS-2OAK in the FSN, and the CS-2OAK can be anywhere within the FSN.

CS-Random Pairs in Pairs.
CS-Random Pairs in Pairs are any two CS-2OAKs, one 2OAK inside another one, the CS-2OAKs can be in any position.

Note: This page contains excerpts and basic information from the book "The Green Guide to Fancy Serial Numbers". Please consider adding a copy to your library, thank you.