The naming of polycyclic alkanes is more complex, with the base name indicating the number of carbons in the ring system, a prefix indicating the number of rings (e.g., "bicyclo"), and a numeric prefix before that indicating the number of carbons in each part of each ring, exclusive of vertices.  For instance, a bicyclooctane which consists of a six-member ring and a four-member ring, which share two adjacent carbon atoms which form a shared edge, is [4.2.0]-bicyclooctane.  That part of the six-member ring, exclusive of the shared edge has 4 carbons.  That part of the four-member ring, exclusive of the shared edge, has 2 carbons.  The edge itself, exclusive of the two vertices that define it, has 0 carbons.