let p, q be sequence of L; :: thesis: p + q = q + p
let n be Element of NAT ; :: according to FUNCT_2:def 8 :: thesis: (p + q) . n = (q + p) . n
thus (p + q) . n = (p . n) + (q . n) by NORMSP_1:def 2
.= (q + p) . n by NORMSP_1:def 2 ; :: thesis: verum