Whenever you use our catalogs, please, give full reference:
Samus N.N., Kazarovets E.V., Durlevich O.V., Kireeva N.N., Pastukhova E.N.,
General Catalogue of Variable Stars: Version GCVS 5.1,
Astronomy Reports, 2017, vol. 61, No. 1, pp. 80-88 {2017ARep...61...80S}
in your papers