pfcConjoin(true,X,X) :- !.
pfcConjoin(X,true,X) :- !.
pfcConjoin(C1,C2,(C1,C2)).


%   File   : pfcdb.pl
%   Author : Tim Finin, finin@prc.unisys.com
%   Author :  Dave Matuszek, dave@prc.unisys.com
%   Author :  Dan Corpron
%   Updated: 10/11/87, ...
%   Purpose: predicates to manipulate a pfc database (e.g. save,
% %     restore, reset, etc.0

% pfcDatabaseTerm(P/A) is true iff P/A is something that pfc adds to
% the database and should not be present in an empty pfc database

pfcDatabaseTerm('$spft$'/3).
pfcDatabaseTerm('$pt$'/2).
pfcDatabaseTerm('$bt$'/2).
pfcDatabaseTerm('$nt$'/3).
pfcDatabaseTerm('==>'/2).
pfcDatabaseTerm('<==>'/2).
pfcDatabaseTerm('<-'/2).
pfcDatabaseTerm(pfcQueue/1).

% removes all forward chaining rules and justifications from db.

pfcReset :-
  pfc_spft(P,F,Trigger),
  pfcRetractOrWarn(P),
  pfcRetractOrWarn('$spft$'(P,F,Trigger)),
  fail.
pfcReset :-
  (pfcDatabaseItem(T)*->
   (pfcError("Pfc database not empty after pfcReset, e.g., ~p.~n",[T]),fail)
    ; true).


% true if there is some pfc crud still in the database.
pfcDatabaseItem(Term:-Body) :-
  pfcDatabaseTerm(P/A),
  functor(Term,P,A),
  clause(Term,Body).

pfcRetractOrWarn(X) :-  retract(X), !.
pfcRetractOrWarn(X) :-
  pfcWarn("Couldn't retract ~p.",[X]),nop((dumpST,pfcWarn("Couldn't retract ~p.",[X]))),!.

pfcRetractOrQuietlyFail(X) :-  retract(X), !.
pfcRetractOrQuietlyFail(X) :-
  nop((pfcTraceMsg("Trace: Couldn't retract ~p.",[X]),nop((dumpST,pfcWarn("Couldn't retract ~p.",[X]))))),
  !,fail.