Inc doesn't mean 'include', it means 'increase'. So you would increase by knitting into the front loop, then into the back loop of the next stitch. A yo leaves a hole as well as putting the inc between two sts, which is what a M1 does too. To get the sts to come out right, you need to kfb which uses a st to inc 1 instead of putting it between sts.
sue- knitting heretic