So only |a-b|=0, |c-a|= 1 or |a-b|= 1, |c-a|=0.

When |a-b|=0 and |c-a|= 1, a=b is obtained.

Substitute | c-a | +| a-b |+b-c| to get 1+0+ 1=2.

When |a-b|= 1 and |c-a|=0, the same result is 0+ 1+ 1=2.