definiens: shall mean the chemical compound known as eszopiclone, also identified by thechemical name ( + ) 6-(5 - chloro-2 - pyridinyl)-6,7 - dihydro-7 - oxo-5H - pyrrolo [ 3,4b ] pyrazin- 5 - yl 4 - methylpiperazine-1 - carboxylate or ( + ) 6-(5 - chloropyri-2 - dyl)-5-(4 - methyl piperazin-1 - yl ) carbonyloxy-7 - oxo-6,7 - dihydro-5H - pyrrolo [ 3,4b]pyrazine, and all pharmaceutically active derivatives thereof, such as, but not limited to, its metabolites, and all esters, salts, hydrates, solvates, polymorphs and isomers of all the above