This is e-pTeX, Version 3.14159265-p3.7-160201-2.6 (utf8.euc) (TeX Live 2016) (preloaded format=platex 2017.1.26)  14 FEB 2018 19:09
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**chapter6.tex
(./chapter6.tex
pLaTeX2e <2016/11/29> (based on LaTeX2e <2017/01/01>)
Babel <3.9r> and hyphenation patterns for 83 language(s) loaded.

./chapter6.tex:3: LaTeX Error: Environment thebibliography undefined.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.
 ...                                              
                                                  
l.3 \begin{thebibliography}
                           {9}
? 
./chapter6.tex:3: Emergency stop.
 ...                                              
                                                  
l.3 \begin{thebibliography}
                           {9}
Your command was ignored.
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or  <return>  to continue without it.

 
Here is how much of TeX's memory you used:
 6 strings out of 493683
 207 string characters out of 6149653
 54216 words of memory out of 5000000
 3672 multiletter control sequences out of 15000+600000
 7511 words of font info for 31 fonts, out of 8000000 for 9000
 929 hyphenation exceptions out of 8191
 5i,0n,4p,67b,16s stack positions out of 5000i,500n,10000p,200000b,80000s
No pages of output.