let z1, z2 be Element of F_Complex ; :: thesis: |.(z1 - z2).| <= |.z1.| + |.z2.|
reconsider z1' = z1, z2' = z2 as Element of COMPLEX by Def1;
z1' - z2' = z1 - z2 by Th5;
hence |.(z1 - z2).| <= |.z1.| + |.z2.| by COMPLEX1:143; :: thesis: verum