TY  - JOUR
T1  - Contributions to Formal Logic. 
JF  - Proceedings of the Royal Society of London (1854-1905)
VL  - 20
SP  - 307
EP  - 308
PY  - 1871/01/01/
UR  - http://dx.doi.org/10.1098/rspl.1871.0060
M3  - doi:10.1098/rspl.1871.0060
AU  - Ellis, A.
ER  -