let z1, z2 be Element of F_Complex; :: thesis: |.(z1 - z2).| <= |.z1.| + |.z2.|
reconsider z19 = z1, z29 = z2 as Element of COMPLEX by Def1;
z19 - z29 = z1 - z2 by Th3;
hence |.(z1 - z2).| <= |.z1.| + |.z2.| by COMPLEX1:57; :: thesis: verum