I skimmed through it. Plenty of clearly written examples and good 
easy-to-read explanations. It could use a bit of grammatical checking 
though.

The example with "There is a animal in your house" would be more 
demonstrative of which of the 4 lines evaluated falsely if there was 
"line 1-4" or part of the match data in the output.

Your mathematical proof contains a zero division error.

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