nomenclature of polycyclic compounds

For the nomenclature of polycyclic compounds,
The main ring is selected so as to include as many skeletal atoms of the polycyclic compound as possible.
A bicyclic system (which comprises the main ring and main bridge only) is named by:the prefix bicyclo- (indicating the number of rings); numbers indicating the bridge lengths (i.e. number of skeletal atoms excluding the bridgehead atoms) separated by full stops and placed in square brackets. The three numbers are cited in decreasing order of size.
The atoms of a bicyclic system are numbered from a bridgehead atom via the longest path to the second bridgehead atom; numbering of atoms continues round the main ring; and then the main bridge atoms are numbered starting from the lower numbered bridgehead atom