could be a typo on line 88 

Line 88 says, "so he can access the variable a just as we'd see before". If we'd means we had, then we need to change the verb to 'seen'. 'before' kind of implies that it can be 'we had seen before'. I have made the change in the pull request.
Merge pull request #19 from varun06/patch-1

Small typo on line 88