Newbie - want to view code for a function

Brand new to R
Want to understand the algorithm used in yule-walker time series 
autoregression model
I assume there is a way to see  the source for ar.yw
I also assume that everybody except me knows how

Could someone suggest to me how to find out

I've looked thru some of the documenttion  - there's a lot - and 
apparently I haven't looked the right place.

Thanks in advance

Dick