let x, y, z be Element of 1; :: thesis: Empty^2-to-zero . (x,z) <= max ((Empty^2-to-zero . (x,y)),(Empty^2-to-zero . (y,z)))
A1: z = {} by CARD_1:49, TARSKI:def 1;
( x = {} & y = {} ) by CARD_1:49, TARSKI:def 1;
hence Empty^2-to-zero . (x,z) <= max ((Empty^2-to-zero . (x,y)),(Empty^2-to-zero . (y,z))) by A1; :: thesis: verum