Chock full of lessons lesson

John gave me one of those lessons where my brain got very, very full.  I'm not sure I'm going to do it justice remembering it all.
First, we talked about the aids for the free walk, following up on our lesson from a few months ago when I realized I had no idea what the aids were.
To ask for the free walk, let the reins slip as I move my hands out.  It is like slip - in/out - slip - in/out (except concurrently).  This way, Duke takes the reins and pulls them down, and I'm not throwing them away and just hoping he drops his head.
To go back to medium walk (oh yeah, start in medium walk before asking for free walk), first bring in the inside rein, then use inside leg to keep him bent, and then bring in outside rein and use outside rein for a half halt (if needed).
This was such an elegant, simple explanation that I should be able to practice it on my own, and I'm sort of horrified for the years I just threw the reins down and then grabbed them back up.
The medium walk should come as you're touching the letter and the rail again, so that if he tries to jig, I can bend him around that inside leg right there on the rail.

From there we did work on the 20 meter and 10 meter circle on bending using my leg aids.  This felt like John got to go a little step further, instead of just repeating himself.  We also did a couple different exercises, where we'd halt, I'd ask him to bend to the inside, and then we'd walk forward.  A few times John had a number of steps (three walk steps, for example) and then trot.  The bending to the inside was just because Duke was stuck in his jaw, and John wanted him to loosen it up.  The key is as soon as he gives with it, to quit jigging around in his face.
John showed me with the reins, how to ask him to the bend to the inside, and then keep the outside firm and then half halt.
Another eureka was not letting my hand drag down and forward, but holding the reins and giving with my elbow (as needed).

John had us on a 20 meter circle, then we'd do 10 meter circles and work on using those leg aids (and a little bit of rein) to make the circle round, then keep that bend and move back out onto the 20 meter circle.  John had a bit more asking him to go forward, but not letting him get long and flat on the forehand.  I felt like I was starting to get the leg aids, steering him around (the flow of water from Sally Swift in Centered Riding?) with my legs, instead of my hands, and then using my hands to get the bend in his neck or in his jaw, but not to steer him (as much) around the circle.
What I'm not as good at is connecting the inside leg to the outside hand - I do the half halt with the rein, but forget the inside leg.
It's very nuanced, and for me - riding every step.  As soon as I let my mind wander (look who drove up, for example), the circle would lose its shape.  Which is good, because that means my legs are working to keep the shape at other times.
A few times, John had me put my inside leg forward, or my outside leg back, and more rarely, to push Duke's haunches in towards John.  This one I can't feel as well, so am not ready to work on at home alone (I don't think).
We would also get a nice trot on the 10 meter circle, then pick up the canter as we rounded the last part of the circle and go out to the 20 meter circle.

It was beautiful weather, like a spring day, which made the contrast with last year when Charlie died very memorable.  Duke rode home without a blanket and got to walk around in his pasture to stretch out without one.  Charlie was in his snow suit last year on this weekend.

I'm frustrated I can't remember more of the lesson but hopefully as I ride this week, I'll feel it and be able to work on it.  I feel like Duke is coming along really well.  Our trot/canter transitions are still a little rough, but he is so much more balanced than when he got here in June, and I feel like we're really communicating better.
Except.  I wanted to go walk him in the sun to cool off, but he got a little anxious about the gate.  Then my idiot brain realized he probably had to leave the chutes when he raced.  (I need to pull his race records.)  So we worked on standing next to it, and swinging it open and shut.  The two times I got impatient and tried to go through it, he wasn't ready.  But I did the same as with the anxious walk/halt, and just stood there and patted him and stayed calm, and eventually he chewed and looked around, and then got less anxious when he realized I wasn't going to ask for anything too crazy.  I guess we just got lucky the one time I rode him through the gate, and we'll have to work on this more at home.

[Edit:  Sure as shit, when I rode Duke tonight I remembered a few more things from the lesson.  One was when Duke "roots" (which is really just like a little tendril, not a real rooting), put both legs on.  If he's stuck in the jaw, counterbend him and then bend him back (that's what we were doing when John took the reins and showed me).  There was more, but now that I'm home and it's been a few hours, I can't remember the other two things.]