implement new disjunction compilation

src/lib/builtins.pl

@@ -218,13 +218,13 @@ fail :- '$fail'.
 %% \+(Goal)
 %
 % True iff Goal fails
-\+ G :- call(G), !, false.
+\+ G :- call(G), !, '$fail'.
 \+ _.
 
 %% \=(?X, ?Y)
 %
 % True iff X and Y can't be unified
-X \= X :- !, false.
+X \= X :- !, '$fail'.
 _ \= _.
 
 

src/lib/format.pl

@@ -513,10 +513,12 @@ portray_clause(Stream, Term) :-
         phrase_to_stream(portray_clause_(Term), Stream),
         flush_output(Stream).
 
+% called once.
 portray_clause_(Term) -->
         { unique_variable_names(Term, VNs) },
         portray_(Term, VNs), ".\n".
 
+% mysteriously called twice, the second time with the truncated B3.
 unique_variable_names(Term, VNs) :-
         term_variables(Term, Vs),
         foldl(var_name, Vs, VNs, 0, _).