# What's wrong with this Proposition 2.10?

My professor said there is an error in proposition 2.10 that he wants me to find. I have been looking at it for a few hours and I still cannot find it. Proposition 2.10 part 1, Proposition 2.10 part 2

• An error in the proposition or in its proof? And what book is this from? – darij grinberg Sep 9 '19 at 2:11
• Related: math.stackexchange.com/questions/218046/… (gives a proof of at least one of the bounds). – darij grinberg Sep 9 '19 at 2:11
• Ah, of course. The $\dfrac{1}{p}+\dfrac{1}{q} = 1$ condition is bull. – darij grinberg Sep 9 '19 at 2:13
• Is it in the equation right before it says “Taking the $p^{th}$ root”, where on the very right it has $||x||_q^{p/q}$? It seems like that should be $||x||_q^{p}$ – Joe Sep 9 '19 at 2:17
• Darij, my professor didn’t not specify whether it is the statement or the proof. To quote him “read the theorem statement and proof of Proposition 2.10 on page 35. Find the ‘glaring error’. This is called numerical linear algebra by Holger Wendland.( isbn is 978-1-316-60117-4) – mattsprestige Sep 9 '19 at 2:37