Exemption scope narrowed: notification excludes supplies between persons specified under section 51(1) clauses (a)-(d), limiting applicability. The amendment inserts a proviso excluding the supply of goods or services or both from the notification's application when the supply takes place between persons specified under clauses (a), (b), (c) and (d) of sub section (1) of section 51 of the Act. The change limits the prior exemption so that supplies among the enumerated government entities and PSUs are not covered. The amendment is deemed effective from the thirty first day of December, 2018.