Spike
Thanks Jeff and I'll try to explain...if I can. Below in quotes and bold are your questions and statements.
"Unfortunately, I cannot understand what you are saying. I don't know what you mean when you say a "downward bend of the pelvis" at address."
I think the pelvis tilts forward from top to bottom when standing erect. Now, forward in golf means left, so I used the word downward and probably should have use the word tilt. But, tilt in golf means left side higher than right side. So therefore my dilemma with wording. So, would it make sense to say that the plevis tilts forward (toward the ball) at address? Not sure, medically that is.
"I also cannot understand how the pelvis can rotate horizontally without tilt during the backswing and downswing. I think that it can only happen during the interval when the hips are squared and weight is equally distributed between each lower limb, and when each lower limb is equally flexed."
I understand what you are saying. But, I was specifically talking about the backswing only. The hips will not stay level during the move forward, for sure. My point being (ignoring the pelvic tilt), that in order for the hips to turn level in the backswing they must have a golf tilt at address(left hip higher than right hip) and the right hip moves in the correct direction with a corresponding knee action. Which would be a deep flex or bend in the right thigh, otherwise the right hip would rise.
"I think that the hips tend to tilt during the hip pivot action, and that the relevant hemi-pelvis (which is being weighted) will tilt up as the pelvis rotates/rocks over the weighted femoral head - because the lower limb on that side is deliberately straightened (rigidified). While that is happening, the unweighted hemi-pelvis will tilt slightly downwards because the relevant lower limb on that side will bend slightly if unweighted. In the backswing, the weighted femoral head is on the right, and the right hemi-pelvis will tilt up;"
This I can understand if there is a lower body weight shift from one foot to the other....nothing wrong with that....it is a way, to be sure. However, in attempting a Level Hip Turn, the weight shift is an upper body condition coupled with the dynamic weight of the swinging clubhead, so to speak. This level hip turn is very effective in counterbalancing the force of the swinging clubhead in a lagging clubhead takeaway.
It also help the shoulders to rotate around the original spine angle and tilt. (That was for you Uncle Dave)
"...while in the late downswing, the left hemi-pelvis will tilt up as it rotates over a straightening left leg. During the early-mid downswing, when the hips are squared, and both lower limbs are roughly equally weighted, then the pelvis can move roughly horizontally, without tilting."
Fair enough.... and in either case of level or tilted hips, in the backswing, there will be a slight bump of the hips forward in the downswing, moving toward the condition you stated above.... I agree....shift happens, man.

So does tilt.
I hope that made it more clear for your analysis, which I really appreciate. Thank you again, you facilitator you.
spike