Merge pull request #70 from jluo117/patch-1

proof theory book for discrete math

Author: mr-mig

README.md

@@ -34,6 +34,7 @@ But knowing the stuff will help you become better! :muscle:*
 - :movie_camera: [UC Berkeley, Data Structures Course](https://archive.org/details/ucberkeley-webcast-PL-XXv-cvA_iAlnI-BQr9hjqADPBtujFJd)
 - [Foundations of Data Structures - EDX](https://www.edx.org/course/foundations-data-structures-iitbombayx-cs213-1x-0#!)
 - [Data Structures - Coursera](https://www.coursera.org/learn/data-structures)
+- [Mathematics for Computer Science - Eric Lehman](https://courses.csail.mit.edu/6.042/spring17/mcs.pdf)
 
 ### Numbers
 - :book: [How to Count](https://www.goodreads.com/book/show/12093869-how-to-count)