eliminate extraneous choice point in $get_attr
'$get_from_list'([L|Ls], V, Attr) :-
nonvar(L),
( L \= Attr -> nonvar(Ls), '$get_from_list'(Ls, V, Attr)
- ; L = Attr, '$enqueue_attr_var'(V)
+ ; L = Attr -> '$enqueue_attr_var'(V)
; '$get_from_list'(Ls, V, Attr)
).
