Floyd Lounsbury described a possible seventh, Dravidian, type of terminological system; there is on-going discussion on whether this system is a sub-type of Iroquois or whether it is a distinct system that had been conflated with Iroquois in Morgan’s typology of kin-term systems. Both systems distinguish relatives by marriage from relatives by descent, although both are classificatory categories rather than being based on biological descent. The basic idea is that of applying an even/odd distinction to relatives that takes into account the gender of every linking relative for ego’s kin relation to any given person. A MFBD(C), for example, is a mother’s father’s brother’s daughter’s child. If each female link (M,D) is assigned a 0 and each male (F,B) a 1, the number of 1s is either even or odd; in this case, even. However, variant criteria exist. In a Dravidian system with a patrilineal modulo-2 counting system, marriage is prohibited with this relative, and a marriageable relative must be modulo-2 odd. There exists also a version of this logic with a matrilineal bias. Discoveries of systems that use modulo-2 logic, as in South Asia, Australia, and many other parts of the world, marked a major advance in the understanding of kinship terminologies that differ from kin relations and terminologies employed by Europeans.