thus (1,2)->(1,?,2) f in PrimRec by Th88; :: according to COMPUT_1:def 19 :: thesis: (1,2)->(1,?,2) f is ternary
thus arity ((1,2)->(1,?,2) f) = 3 by Def27; :: according to COMPUT_1:def 27 :: thesis: verum