SPOJ:XMAX(gaussian elimionation)

Any one please explain how gausssian elimination in order to find the maximum xor subset over an array?</pre?
[https://www.hackerearth.com/notes/gaussian-elimination/][1]
I read the tutorial here but i was not unable to understand how GE works here.

  [1]: https://www.hackerearth.com/notes/gaussian-elimination/
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