**
REVIEWS
**

- Michael Berg
[Mathematical Association of America Reviews]
**This book has to be seen to be believed**[4 Sep 2008] - J. Moldovan
[amazon.com]
**A beautiful work you must have**[23 Oct 2008] - Abstrusegoose.com
**My Fellow Mathematicians and Physicists**[16 Mar 2009]

[click through the next 2 frames] “Actually, I don’t know anyone who has adopted Penrose’s diagrammatic tensor notation, but it seems to work well enough.”

If the joke is too abstruse for you: There 3 frames are about 3 notations for inner product of two vectors O.X (to use 4th notation). Amusingly, the “mathematical notation” was introduced by Dirac, and physicist's notation by someone like Cartan or earlier. Abstrusegoose.com explains: "know" in the sense of "met". I never "met" anyone who uses Penrose's notation. Of course I "know of" people who use it (not the least of whom is Sir Roger Penrose himself :) ).

**
BLOGS
**

- Elisha Peterson, Qiaochu Yuan, Greg Kuperberg and others
**trace diagrams, tensor diagrams, arrow notation, ...**[20 Nov 2009] - José Antonio Ortega Ruiz
[physics musings]
**Geometrically speaking**[6 Jul 2006] - John Baez
[This Week's Finds in Mathematical Physics]
**This intro to Lie groups is also a bit quirky**[24 Dec 2007]**Diagrammatic approach to Clebsch-Gordan coefficients**[6 Feb 2001]:

"a really cool book by a guy named something like Ctanovic, which is presently almost impossible to find unless you're a wizard. (This book will eventually be published more widely, after what's-his-name inserts a section on diagram techniques for exceptional Lie groups!)"

What's-his-name Ctanović responds: "True fact: I had a dinner once at a friends' house with Joan Baez, but I declined her offer of a ride home as I was on a bicycle." - Hasten Jason, El Naschie Watch
**This surfer is no Einstein**[8 Mar 2010]

"The magic square did it! His colleague Prof. P. Cvitanović, a student of another extragalactic like El Naschie is saying the same." - Alejandro Rivero
- "And it could even happen that all the recent rage on reviewing the properties of scattering amplitudes and looking for general properties of Feynman diagrams could be remotely inspired in Cvitanovic flirt with Madness."

- Roger Penrose [29 Oct 1981]: invented this notation in 1952.

P Cvitanović: "No contest - as a late starter, I got into the first grade in fall of 1953, drawing pretty much the same kind of drawings. But I did refer to the one Penrose diagrammatic paper I knew about in my 1976 Phys Rev paper, refs 38, 39." - Pierre Deligne [6 Dec 1996]: "I am most intrigued by your Magic Triangle, p. 9 of your Group Theory book."
- Ben Mottelson [15 Sept 1999]: Unsang heroes.
- David Mermin [29 Dec 2002]: "Don't know how much further I'll get, but ..."
- Roger Penrose [4 Jan 2003]: "There will be some bird-tracks (or fornicating ostriches, as one of my colleagues prefers to call them) in my book too"
- Tony Smith [17 Feb 2003]: "where was the Magic Triangle first discussed?"
- Dorte Glass [21 Nov 2008]: "... at sidde og tyde dine hieroglyffer..."
- Rob Pisarski: "What you do is the 't Hooft basis, right?"