TITLE: Proof of Witt's result about quaternion extensions
QUESTION [8 upvotes]: I'm searching for a proof of Witt's result that a biquadratic extension $K(\sqrt{a},\sqrt{b})/K$ extends to a Galois extension $L/K$ with quaternion group $Q_8$ iff the quadratic forms $<a,b,\frac{1}{ab}>, <1,1,1>$ are equivalent iff $(a,b)(a,a)(b,b) = 0 \in Br(K)$.
I know there is a proof in his original paper "Konstruktion von galoisschen Körpern der Charakteristik p zu vorgegebener Gruppe der Ordnung pf". However, I am searching for a proof in English. I would also like to find proofs from a more modern perspective as well as generalizations of the result.
Thank you.

REPLY [7 votes]: A complete proof can be found in the first few pages of
https://mathscinet.ams.org/mathscinet-getitem?mr=977759
Jensen, Christian U.(DK-CPNH); Yui, Noriko(3-TRNT)
Quaternion extensions. Algebraic geometry and commutative algebra, Vol. I, 155–182, Kinokuniya, Tokyo, 1988. 
I will scan the relevant pages and post them here as soon as electricity is restored in my office.
Addendum: Here is the paper :
https://drive.google.com/open?id=0B8EHtI8F9qdIODNpZTQ1c1JjQTlIUUdsWm1nZmxRWVNTM1Bj