How many math books in the stack?

Let's see how correct you all are.

How many math books in the stack?
Updates
9 mo
There are 7 math books, you can see 6 of them already, the 7th one is the one under Macroeconomics. If you see closely, zoom in and stuff, then you can see the initials letters 'mat' clearly and shadow kind of impression of rest letters. @AnrgyCarl2 got it right first followed by @InknKink. You guys win!
Updates
9 mo
How many math books in the stack?
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