題組內容

(1)[5+10+10分]A function d:M x M → 10,[0,∞) is called an uitrametric if
● d(x, y) = 0 if and only if x = y;
●d(x,y) =d(y,x);
●d(x,z) ≤ max(d(x,y),d(y, z)}
for any t,y,z615ba9a786d2f.jpg M. We call (M,d) an ultrametric space.

(a) Show that an ultrame etric space, (M,d), is a metric space.