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. Author manuscript; available in PMC: 2009 Jan 1.
Published in final edited form as: Trends Cogn Sci. 2007 May 1;11(6):236–242. doi: 10.1016/j.tics.2007.04.001

Table 1. Arity of relations, number of slots or variables, an example of each level and approximate median age of attainment.

Arity of relation Slots/variables Example Median age
Unary one class membership, e.g. cat(Marcus) One year
Binary two larger(elephant, mouse) 1½ years
Ternary three addition(2,3,5) 5 years
Quaternary four proportion( 2,3,6,9) 11 years