# Single bar in Cauchy Schwarz

I need to write out the proof for the Cauchy-Schwarz equation from quantum computing. I'm stuck on the first step as I don't understand what the single bars on the first term in the equation. Double bars is length but single??

http://en.wikipedia.org/wiki/Cauchy–Schwarz_inequality

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diazona
Homework Helper
Single bars indicate the absolute value, or magnitude.

For the record, it's not uncommon for people to use single bars to designate the norm (length) of a vector, even though the proper notation is technically double bars.

Thanks I was totally stuck, as in all the notes the professor used double bars.