take M0 = MetrStruct(# 1,Empty^2-to-zero #); ( M0 is strict & M0 is ultra & M0 is Reflexive & M0 is symmetric & M0 is Discerning & M0 is triangle )
M0 is ultra
proof
let x,
y,
z be
Element of
M0;
METRIC_1:def 20 dist x,z <= max (dist x,y),(dist y,z)
thus
dist x,
z <= max (dist x,y),
(dist y,z)
by Th8;
verum
end;
hence
( M0 is strict & M0 is ultra & M0 is Reflexive & M0 is symmetric & M0 is Discerning & M0 is triangle )
; verum