[...] (54) a. RR I,[CASE:acc]([σ]) = [σ]/[CASE:nom] CLASS: Nounal; b. RR I,[NUM:pl]([σ]) = [σ]/GEN:fem, NUM:sg] CLASS: Nounal [...]. The rules of referral in 54a and 54b are "commutative" in the sense that the composite of 54a with 54b is the same function as the composite of 54b with 54a. - Stump (2004), a pag.124-125