Corrections and comments to "Introduction to Number Theory" by M. Klazar
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p. 38. In Euler's identity, replace x_1y_3-x_3y_1 with -x_1y_3+x_3y_1.

p. 38. In the beginning of the arithmetic proof of the four squares theorem, 
replace -a^2 with -a^2-1, and  
a^2+b^2=a^2+b^2+0^2+0^2 with a^2+b^2+1=a^2+b^2+1^2+0^2, i.e., Lemma must be 
used exactly as stated. One has to exclude the trivial solution a=b=0.

p. 44 and elsewhere. infinititude -> infinitude  


(November 2006)