M=Rn and d((x1,…,xn),(y1,…,yn))=1≤i≤nmax∣xi−yi∣
M={a,b,c,d}, where d(a,b)=d(a,c)=3, d(a,d)=d(b,c)=7, and d(b,d)=d(c,d)=11
M=C[0,1], the set of continuous functions [0,1]→R, and d(f,g)=x∈[0,1]max∣f(x)−g(x)∣
M=C[0,1] and d(f,g)=∫01(f(x)−g(x))2dx