🚀 go-pugleaf

I got answers from F. Kluzniak, R. K. Horsell, F. Pereira, K. Verschaetse,
L. Naish, R. O'Keefe, M. Brady and R. McEntire (chronological order):
my thanks to all of them

people seem to agree that in a correct implementation of immediate update view,
the results should be

question 1:

?- [user].
| a(1).
| user consulted 68 bytes 3.97364e-09 sec.

yes
?- a(X) , write(X) , retract(a(1)) , asserta(a(2)) , fail .
1
no


question 2:

| ?- [user].
| a(1).
| user consulted 68 bytes 3.97364e-09 sec.

yes
| ?- a(X) , write(X) , retract(a(1)) , assertz(a(2)), fail.
12
no

and I am very happy about this: the meaning of asserta and assertz is
different even when there are no (non-retracted) clauses

some systems that implementent the immediate update view correctly:

	DEC-10 DEC-20 Prolog
	CProlog in debug mode (not in non-debug mode)
	R. K. Horsell's own implementation(s) (about which I know nothing more)
	Quintus Prolog 1.x (the current Quintus version has logical view)

my questions were related to a gap in the specification of database updates
in Prolog (for ISO)
I now am reassured that I tried to fill the gap in a way people agree with

Bart Demoen