used in some classification systems: a group of extinct fossil gymnosperms coextensive with the order Cycadofilicales
used in some classification systems: a group of extinct fossil gymnosperms coextensive with the order Cycadofilicales
any number of entities (members) considered as a unit
(chemistry) two or more atoms bound together as a single unit and forming part of a molecule
a set that is closed, associative, has an identity element and every element has an inverse
