The Alternating Half Double Crochet Increase stitch is easier than it sounds. It is simply working one half double crochet into the front loop of the indicated stitch and then working a second half double crochet into the back loop of the same stitch. So two half double crochets in one stitch which creates in increase, but still keeps with the alternating pattern of front loop, back loop.
Half Double Crochet Two Together (hdc2tog) Photo Tutorial
This tutorial is not for the traditional half double crochet 2 together stitch that uses both loops on both stitches. You are still creating a decrease in stitches, but this special stitch uses the front loop of the first stitch and the back loop of the next stitch or vice versa. It’s used in the pattern called the Aspen Tweed Hat.