12.
From 11, we have: 1. Norm implies convex norm ball.
Hence the contra positive of the statement will state that, if the norm ball is not convex, then it's not a norm.
12.
From 11, we have: 1. Norm implies convex norm ball.
Hence the contra positive of the statement will state that, if the norm ball is not convex, then it's not a norm.
6.