copy_term(ParentRule,ParentRuleCopy),
  buildRhs(Head,Rhs),
  current_why_U(USER), % @TODO REVIEW _U
  pfcForEach(pfc_nf(Body,Lhs),
          (buildTrigger(Lhs,rhs(Rhs),Trigger),
           pfcAdd('$bt$'(Head,Trigger),(ParentRuleCopy,USER)))).
get_bc_clause(Head,(HeadC:- BodyC)):- get_bc_clause(Head,HeadC,BodyC).

get_bc_clause(HeadIn, ~HeadC, Body):- compound(HeadIn), HeadIn = ~Head,!,
     Body = ( awc,
            ( nonvar(HeadC)-> (HeadC = Head,!) ; (HeadC = Head)),
              pfc_bc_and_with_pfc(~Head)).
get_bc_clause(Head, Head, Body):-  % % :- is_ftNonvar(Head).
     Body = ( awc, !, pfc_bc_and_with_pfc(Head)).

:- thread_initialization(nb_setval('$pfc_current_choice',[])).

push_current_choice:- current_prolog_flag(pfc_support_cut,false),!.
push_current_choice:- prolog_current_choice(CP),push_current_choice(CP),!.
push_current_choice(CP):- nb_current('$pfc_current_choice',Was)->b_setval('$pfc_current_choice',[CP|Was]);b_setval('$pfc_current_choice',[CP]).

cut_c:- current_prolog_flag(pfc_support_cut,false),!.
cut_c:- must_ex(nb_current('$pfc_current_choice',[CP|_WAS])),prolog_cut_to(CP).


% % 
% %
% %  eval something on the LHS of a rule.
% %


fcEvalLHS((Test->Body),Support) :-
  !,
  pfcDoAll(pfcCallSystem(Test) -> (fcEvalLHS(Body,Support))),
  !.

fcEvalLHS((Test*->Body),Support) :-
  !,
  pfcDoAll(pfcCallSystem(Test) *-> (fcEvalLHS(Body,Support))).

fcEvalLHS(rhs(X),Support) :-
  !,
  pfcDoAll(pfc_eval_rhs(X,Support)),
  !.

fcEvalLHS(X,Support) :-
  pfcType(X,trigger(_Pos)),
  !,
  pfcAddTrigger(X,Support),
  !.

%fcEvalLHS(snip(X),Support) :-
%  snip(Support),
%  fcEvalLHS(X,Support).

fcEvalLHS(X,_) :-
  pfcWarn("Unrecognized item found in trigger body, namely ~p.",[X]).


% %
% %  eval something on the RHS of a rule.
% %

pfc_eval_rhs([],_) :- !.
pfc_eval_rhs([Head|Tail],Support) :-
  pfc_eval_rhs1(Head,Support),
  pfc_eval_rhs(Tail,Support).


pfc_eval_rhs1(Fact,S) :- control_arg_types(Fact,Fixed),!,pfc_eval_rhs1(Fixed,S).

pfc_eval_rhs1({Action},Support) :-
 % evaluable Prolog code.
 !,
 fcEvalAction(Action,Support).

pfc_eval_rhs1(P,_Support) :-
 % predicate to remove.
 pfcNegatedLiteral(P),
 !,
 pfcWithdraw(P).

pfc_eval_rhs1([X|Xrest],Support) :-
 % embedded sublist.
 !,
 pfc_eval_rhs([X|Xrest],Support).

pfc_eval_rhs1(Assertion,Support) :-
 % an assertion to be added.
  once_writeq_nl(pfcRHS(Assertion)),
 (must_ex(pfcPost1(Assertion,Support))*->true ;
   pfcWarn("Malformed rhs of a rule: ~p",[Assertion])).


% %
% %  evaluate an action found on the rhs of a rule.
% %

fcEvalAction(Action,Support) :-
  pfcCallSystem(Action),
  (undoable(Action)
     -> pfcAddActionTrace(Action,Support)
      ; true).


% %
% %
% %

trigger_trigger(Trigger,Body,_Support) :-
 trigger_trigger1(Trigger,Body).
trigger_trigger(_,_,_).


%trigger_trigger1(presently(Trigger),Body) :-
%  !,
%  copy_term(Trigger,TriggerCopy),
%  pfc_call(Trigger),