 "Dinor" does not have to be reduction in adjacent carbons e.g.5-Acetyl-4,18-dinor-retinoic acid, where 4 referred to a ring carbon and 18 referred to a methyl group on the 5th carbon on the ring.The alternative use of "nor", in naming the unbranched form of a compound within a series of isomers (also referred to as "normal") is obsolete and not allowed in IUPAC names.