And so some of the math we'll see in deriving factor analysis will be a little bit different than what you saw before and they're just a - it turns out the full derivation for EM for factor analysis is sort of extremely long and complicated and so I won't inflect that on you in lecture today, but I will still be writing more equations than is - than you'll see me do in other lectures because there are, sort of, just a few steps in the factor analysis derivation so I'll physically illustrate it. 