There are a few similar slip-ups in the article; the author is presumably not a native English speaker. However, despite that - and what really motivated me to comment - I find this really well written, and the odd mistake just adds a bit of character. Very impressed.

True, I am not a native English speaker (French here). Doing my best to fix all those tiny typos. Any report appreciated. :)

Now fixed. My apologies for the awful typo. :)