[43] Schwarz Inequality: For any x,y∈R^n, |(x|y)| ≦ |x||y| (the equality holds only if tx = y for some t∈R.)

https://www.evernote.com/shard/s29/sh/689a6187-d66b-4e6c-8fd8-d681267fd5f0/5a90346efdf827ddbc6ad9ab00d2a663