This question is related to visibility of lattice points from textbook Apostol Introduction to analytic number theory ( Chapter 3) .
Apostol defines Two lattice Points P and Q are called mutually visible if the line segment joining them contains no lattice points other than endpoints P and Q.
Then Apostol writes
It is clear that (a, b) and (m, n) are mutually visible iff (a-m, b-n) is visible from origin.
Can someone please tell how to prove this statement.