🚀 go-pugleaf

Hello,
I need a clarification on the following put instruction please.
I shall use D.H.Warren's notation from his paper An Abstract Prolog 
Instruction Set. 
put_variable Xn|Yn,Ai :
	For Yn the paper lists the following assignment:
	Ai := Yn := ref_to(Yn)
	For Xn it lists the following:
	Ai := Xn := next_term(H) := tag_ref(H)

Question 1: For the Yn case, ref_to(Yn) puts in Ai a tagged reference or just
	    the address of Yn without tag?
Question 2: For the Xn case, Ai, and Xn get the current heap pointer converted
	    to a tagged reference, or its raw value? Which is executed first?
	    next_term or tag_ref. Compare this with the description of
	    put_structure where it is stated the following:
	    Ai := tag_struct(H)
	    next_term(H) := F (the functor)

I shall appreciate any kind of information. Thanks in advance,

Vassilios E. Axaris
SUNY Buffalo Computer Engineering.