add Lab6_Notes.ipynb
add DH position to Prob 1(L) in HW3.ipynb
fixed typos in HW3.ipynb
fixed typo in Lab6
fixed year typo in Prob 1(f) in HW3
upload Lab7_Note.ipynb
updated last section in Lab 7
updated links after Lab6
added Lecture12-Confounding.ipynb from 2014-10-09
added HW3-solutions.ipynb
added HW4.ipynb
fixed Problem 2(a): changed n_M to n_1
Merge remote-tracking branch 'upstream/master'