% ----------------------------------------------------------------------
% $Id: clsimpl.red,v 1.11 1999/04/13 13:11:01 sturm Exp $
% ----------------------------------------------------------------------
% Copyright (c) 1995-1999 Andreas Dolzmann and Thomas Sturm
% ----------------------------------------------------------------------
% $Log: clsimpl.red,v $
% Revision 1.11 1999/04/13 13:11:01 sturm
% Updated comments for exported procedures.
%
% Revision 1.10 1999/03/22 17:06:43 dolzmann
% Changed copyright information.
% Added and reformatted comments.
%
% Revision 1.9 1999/03/21 13:34:45 dolzmann
% Added the cl-part of the super simplifier susi.
%
% Revision 1.8 1999/01/17 15:36:43 dolzmann
% Corrected some typos in the comments.
%
% Revision 1.7 1997/08/24 16:14:56 sturm
% Added procedure cl_sitheo using fluid !*rlsithok.
% Added service rl_surep with black box rl_multsurep.
% Added service rl_siaddatl.
%
% Revision 1.6 1996/10/07 11:45:55 sturm
% Added fluids for CVS and copyright information.
%
% Revision 1.5 1996/09/05 11:50:11 dolzmann
% Minor changes in procedure cl_simplat.
%
% Revision 1.4 1996/09/05 11:14:20 dolzmann
% Fixed a bug in cl_simplat: atomic formulas are always simplified.
%
% Revision 1.3 1996/07/13 11:01:59 dolzmann
% Fixed a bug in cl_simpl.
% Introduced new black box rl_smcpknowl.
% Removed procedure cl_cpknowl.
% Added context independent black box implementations cl_smcpknowl,
% cl_smrmknowl, cl_smupdknowl, cl_smmkatl, cl_smsimpl!-impl, and
% cl_smsimpl!-equiv1.
%
% Revision 1.2 1996/03/25 08:50:55 sturm
% Fixed a bug in procedure cl_simpl.
%
% Revision 1.1 1996/03/22 10:31:32 sturm
% Moved and split.
%
% ----------------------------------------------------------------------
lisp <<
fluid '(cl_simpl_rcsid!* cl_simpl_copyright!*);
cl_simpl_rcsid!* := "$Id: clsimpl.red,v 1.11 1999/04/13 13:11:01 sturm Exp $";
cl_simpl_copyright!* := "(c) 1995-1999 by A. Dolzmann and T. Sturm"
>>;
module clsimpl;
% Common logic simplification routines. Submodule of [cl]. Here the
% standard simplifier is implemented.
%DS
% <theory> ::= (<atomic_formula>,...)
procedure cl_simpl(f,atl,n);
% Common logic simplify. [f] is a formula; [atl] is a list of
% atomic formulas, which are considered to describe a theory; [n]
% is an integer. Depends on switches [!*rlsism], [!*rlsichk],
% [!*rlsiso], [!*rlsiidem]. Returns the identifier [inctheo] or a
% formula. [inctheo] means that [atl] is inconsistent. Else the
% result is [f], simplified (wrt. [atl]). For non-negative [n],
% simplification stops at level [n].
begin scalar w;
if null !*rlsism then
return cl_simpl1(f,nil,n,nil);
atl := cl_sitheo atl;
if atl eq 'inctheo then
return 'inctheo;
w := rl_smupdknowl('and,atl,nil,n+1);
if w eq 'false then return 'inctheo;
return cl_simpl1(f,w,n,nil)
end;
procedure cl_sitheo(atl);
% Common logic simplify theory. [atl] is a THEORY. Returns either a
% list $l$ of atomic formulas, or the identifier [inctheo]. In the
% first case the conjunction over $l$ is equivalent to the
% conjuction over [atl], and $l$ contains only simplified atomic
% formulas. The return value [inctheo] means that the conjunction
% over [atl] is equivalent to [false]. Accesses the fluid
% [rlsithok], and returns [atl] in case that [rlsithok] is
% non-[nil].
begin scalar atf,w,natl,!*rlsiexpla;
if !*rlsithok then
return atl;
while atl do <<
atf := car atl;
atl := cdr atl;
w := cl_simplat(atf,nil);
if w eq 'false then <<
atf := 'inctheo;
atl := nil
>> else if w neq 'true then
natl := w . natl
>>;
if atf eq 'inctheo then
return 'inctheo;
return natl
end;
procedure cl_simpl1(f,knowl,n,sop);
% Common logic simplify. [f] is a formula; [knowl] is an IRL; [n]
% is an integer; [sop] is a CL operator. Depends on switches
% [!*rlsism], [!*rlsichk], [!*rlsiso], [!*rlsiidem]. Returns a
% formula. Simplifies [f] recursively using [knowl].
begin scalar op,result,w,newknowl;
if eqn(n,0) then return f;
op := rl_op f;
if rl_tvalp op then return f;
if rl_junctp op then
return rl_smkn(op,cl_smsimpl!-junct(op,rl_argn f,knowl,n));
if op eq 'not then <<
result := cl_simpl1(rl_arg1 f,knowl,n-1,'not);
if rl_tvalp result then return cl_flip result;
if cl_atfp result then return rl_negateat result;
return cl_negate!-invol(result)
>>;
if rl_quap op then <<
if !*rlsism then knowl := rl_smrmknowl(knowl,rl_var f);
result := cl_simpl1(rl_mat f,knowl,n-1,op);
if rl_tvalp result then return result;
return rl_mkq(op,rl_var f,result)
>>;
if op eq 'impl then
return cl_smsimpl!-imprep(rl_arg2l f,rl_arg2r f,knowl,n);
if op eq 'repl then
return cl_smsimpl!-imprep(rl_arg2r f,rl_arg2l f,knowl,n);
if op eq 'equiv then
return cl_smsimpl!-equiv(rl_arg2l f,rl_arg2r f,knowl,n);
w := cl_simplat(f,sop);
if !*rlsism then <<
op := rl_op w;
if rl_junctp op then
return rl_smkn(op,cl_smsimpl!-junct(op,rl_argn w,knowl,n));
if rl_tvalp op then
return w;
% [w] is atomic.
newknowl := rl_smupdknowl('and,{w},rl_smcpknowl knowl,n);
if newknowl eq 'false then return 'false;
w := rl_smmkatl('and,knowl,newknowl,n);
return rl_smkn('and,w)
>>;
if w then return w;
rederr {"cl_simpl1(): unknown operator",op}
end;
procedure cl_negate!-invol(f);
% Common logic negate applying the law of involutivity. [f] is a
% formula. Returns $\phi$ if [f] is of the form $\lnot \phi$,
% $\lnot [f]$ else.
if rl_op f eq 'not then rl_arg1 f else rl_mk1('not,f);
procedure cl_gand!-col(fl,n,gand,knowl);
% Common logic generic ['and] collect. [fl] is a list of formulas;
% [n] is an integer; [gand] is one of ['and], ['or]; [knowl] is an
% IRL. Depends on switch [!*rlsichk]. Returns a list $l$ of
% simplified formulas such that $[gand](l)$ is equivalent to
% $[gand]([fl])$. With [!*rlsichk] on, $l$ does not contain any
% double entries. Moreover there are no truth values in $l$, and no
% element of $l$ has [gand] as its top-level operator.
begin scalar result,a,gtrue,gfalse;
gtrue := cl_cflip('true,gand eq 'and);
gfalse := cl_flip(gtrue);
while fl do <<
a := cl_simpl1(car fl,knowl,n-1,gand);
fl := cdr fl;
if a eq gfalse then <<
result := {gfalse};
fl := nil
>> else if a neq gtrue then
if rl_op a eq gand then <<
if !*rlsichk then
for each subf in rl_argn a do
(if not (subf member result) then
result := subf . result)
else
for each subf in rl_argn a do
result := subf . result
>> else
if not (!*rlsichk and a member result) then
result := a . result;
>>;
return if result then reversip result else {gtrue}
end;
procedure cl_smsimpl!-junct(op,junct,knowl,n);
% Common logic smart simplify. [op] is one of [and], [or]; [junct]
% is a list of formulas; [knowl] is an IRL; [n] is an integer.
% Returns a list of formulas. Accesses the switch [!*rlsism]. With
% [!*rlsism] on sophisticated simplifications are applied to
% [junct].
begin scalar break,w,atl,col,newknowl;
if not !*rlsism then
return cl_gand!-col(junct,n,op,nil);
newknowl := rl_smcpknowl knowl;
break := cl_cflip('false,op eq 'and);
for each subf in junct do <<
w := if cl_atfp subf then cl_simplat(subf,op) else subf;
if cl_atfp w then atl := w . atl else col := w . col
>>;
newknowl := rl_smupdknowl(op,atl,newknowl,n);
if newknowl eq 'false then return {break};
return cl_smsimpl!-junct1(op,atl,reversip col,knowl,newknowl,n,break)
end;
procedure cl_smsimpl!-junct1(op,atl,col,knowl,newknowl,n,break);
% Common logic smart simplify. [op] is one of [and], [or]; [atl] is
% a list of atomic formulas; [col] is a list of complex formulas;
% [knowl] and [newknowl] are IRL's; [n] is an integer; [break] is
% one of [true], [false] corresponding to [op]. Returns a list of
% formulas.
begin scalar a,w,wop,argl,sicol,natl;
while col do <<
a := car col;
col := cdr col;
w := cl_simpl1(a,newknowl,n-1,op);
wop := rl_op w;
if wop eq break then <<
a := break;
col := nil
>> else if wop eq op then <<
argl := rl_argn w;
while argl and cl_atfp car argl do <<
natl := car argl . natl;
argl := cdr argl
>>;
if !*rlsiidem and natl then <<
col := nconc(reversip sicol,col);
sicol := nil
>>;
sicol := nconc(sicol,reverse argl) % necessarily constructive!
>> else if rl_cxp wop then
(if wop neq cl_flip break then sicol := w . sicol)
else << % [w] is atomic.
if !*rlsiidem then <<
col := nconc(reversip sicol,col);
sicol := nil
>>;
natl := {w}
>>;
if natl then <<
newknowl := rl_smupdknowl(op,natl,newknowl,n);
if newknowl eq 'false then <<
a := break;
col := nil
>>;
natl := nil
>>
>>;
if a eq break then return {break};
return cl_smsimpl!-junct2(op,sicol,knowl,newknowl,n,break)
end;
procedure cl_smsimpl!-junct2(op,sicol,knowl,newknowl,n,break);
% Common logic smart simplify. [op] is one of [and], [or]; [col] is
% a list of complex formulas; [knowl] and [newknowl] are IRL's; [n]
% is an integer; [break] is one of [true], [false] corresponding to
% [op]. Returns a list of formulas.
begin scalar atl,w;
atl := rl_smmkatl(op,knowl,newknowl,n);
if !*rlsichk then <<
w := sicol;
sicol := nil;
for each x in w do sicol := lto_insert(x,sicol)
>> else
sicol := reversip sicol;
if !*rlsiso then atl := sort(atl,'rl_ordatp);
w := nconc(atl,sicol);
if w then return w;
return {cl_flip break}
end;
procedure cl_smsimpl!-imprep(prem,concl,knowl,n);
% Common logic smart simplify implication/replication. [prem] and
% [concl] are formulas; [knowl] is an IRL; [n] is an integer.
% Returns a formula equivalent to [prem impl concl] assuming
% [knowl].
begin
if not !*rlsism then
return cl_imprep!-col(prem,concl,knowl,n);
if cl_atfp prem then
prem := cl_simplat(prem,'prem);
if cl_atfp concl then
concl := cl_simplat(concl,'concl);
if prem eq 'false or concl eq 'true then
return 'true;
return cl_smsimpl!-imprep1(prem,concl,knowl,n)
end;
procedure cl_imprep!-col(prem,concl,knowl,n);
begin scalar w;
prem := cl_simpl1(prem,knowl,n-1,'prem);
concl := cl_simpl1(concl,knowl,n-1,'concl);
if w := cl_smtvchk!-impl(prem,concl) then
return w;
if prem = concl then return 'true;
return rl_mk2('impl,prem,concl)
end;
procedure cl_smsimpl!-imprep1(prem,concl,knowl,n);
% Common logic smart simplify implication/replication. [prem] and
% [concl] are formulas; [knowl] is an IRL; [n] is an integer.
% Returns a formula equivalent to [prem impl concl] assuming
% [knowl].
begin scalar w;
if cl_atfp prem then
return cl_smsimpl!-imprep!-atprem(prem,concl,knowl,n);
if cl_atfp concl then
return cl_smsimpl!-imprep!-atconcl(prem,concl,knowl,n);
prem := cl_simpl1(prem,knowl,n-1,'prem);
concl := cl_simpl1(concl,knowl,n-1,'concl);
if w := cl_smtvchk!-impl(prem,concl) then
return w;
if cl_cxfp prem and cl_cxfp concl then <<
if !*rlsichk and prem = concl then
return 'true;
return rl_mk2('impl,prem,concl)
>>;
return cl_smsimpl!-imprep1(prem,concl,knowl,n)
end;
procedure cl_smtvchk!-impl(prem,concl);
if prem eq 'true then
concl
else if concl eq 'false then
cl_simpl(rl_mk1('not,prem),nil,1)
else if prem eq 'false or concl eq 'true then
'true;
procedure cl_smsimpl!-imprep!-atprem(atprem,concl,knowl,n);
begin scalar w,newknowl;
newknowl := rl_smcpknowl knowl;
if cl_atfp concl then
return rl_smsimpl!-impl(atprem,concl,knowl,newknowl,n);
newknowl := rl_smupdknowl('and,{atprem},newknowl,n);
concl := cl_simpl1(concl,newknowl,n-1,'concl);
if w := cl_smtvchk!-impl(atprem,concl) then
return w;
if cl_atfp concl then
return rl_smsimpl!-impl(atprem,concl,knowl,newknowl,n);
return rl_mk2('impl,atprem,concl)
end;
procedure cl_smsimpl!-imprep!-atconcl(prem,atconcl,knowl,n);
% CL smart simplify implication/replication with atomic formula
% conclusion. [prem] is a complex formula; [atconcl] is a
% simplified atomic formula; [knowl] is an IRL; [n] is an integer.
% Returns a formula.
begin scalar w,newknowl;
newknowl := rl_smupdknowl('or,{atconcl},rl_smcpknowl knowl,n);
prem := cl_simpl1(prem,newknowl,n-1,'prem);
if w := cl_smtvchk!-impl(prem,atconcl) then
return w;
if cl_atfp prem then
return rl_smsimpl!-impl(prem,atconcl,knowl,newknowl,n);
return rl_mk2('impl,prem,atconcl)
end;
procedure cl_smtvchk!-equiv(lhs,rhs);
if lhs eq 'true then
rhs
else if rhs eq 'true then
lhs
else if lhs eq 'false then
cl_simpl(rl_mk1('not,rhs),nil,1)
else if rhs eq 'false then
cl_simpl(rl_mk1('not,lhs),nil,1);
procedure cl_smsimpl!-equiv(lhs,rhs,knowl,n);
begin scalar w,newknowl;
lhs := cl_simpl1(lhs,knowl,n-1,'equiv);
rhs := cl_simpl1(rhs,knowl,n-1,'equiv);
if w := cl_smtvchk!-equiv(lhs,rhs) then
return w;
if !*rlsichk and lhs = rhs then
return 'true;
if null !*rlsism or cl_cxfp lhs or cl_cxfp rhs then <<
if cl_ordp(lhs,rhs) then
return rl_mk2('equiv,lhs,rhs);
return rl_mk2('equiv,rhs,lhs)
>>;
newknowl := rl_smcpknowl(knowl);
return rl_smsimpl!-equiv1(lhs,rhs,knowl,newknowl,n)
end;
procedure cl_ordp(f1,f2);
% Common logic order predicate. [f1] and [f2] are formulas. Returns
% [T] or [nil]. [nil] is returned if [f1] and [f2] are atomic
% formulas and [f1] is less than [f2] wrt. [rl_ordatp].
cl_cxfp f2 or (cl_atfp f1 and rl_ordatp(f1,f2));
procedure cl_simplat(atf,sop);
% Common logic simplify atomic formula. [atf] is an atomic formula;
% [sop] is a CL operator. Returns a quantifier-free formula
% equivalent to [atf].
if not !*rlidentify then
rl_simplat1(atf,sop)
else
cl_apply2ats(rl_simplat1(atf,sop),'cl_identifyat);
procedure cl_identifyat(atf);
% Common logic identify atomic formula. [atf] is an atomic formula.
% Returns an atomic formula equal to [atf].
begin scalar w;
if rl_tvalp atf then return atf;
if (w := atf member cl_identify!-atl!*) then return car w;
cl_identify!-atl!* := atf . cl_identify!-atl!*;
return atf
end;
% The following code implements a "generic smart simplification". All
% black boxes for the smart simplification are implemented generically
% using only a non generic black box rl_negateat. rl_negateat must
% return an atomic formula.
procedure cl_smcpknowl(knowl);
% Common logic smart simplifier copy knowledge. [knowl] is a
% knowledge base. Returns a toplevel copy of [knowl].
for each p in knowl collect p;
procedure cl_smrmknowl(knowl,v);
% Common logic smart simplifier remove knowledge. [knowl] is a
% knowledge base; [v] is a variable. Returns a knowledge base.
% Removes all knowledge involving [v] from the knowledge base.
nil;
procedure cl_smupdknowl(op,atl,knowl,n);
% Common logic smart simplifier update knowledge. [op] is one of
% the operators [and], [or]; [atl] is a list of atomic formulas;
% [knowl] is knowledge base; [n] is an integer. Returns a knowledge
% base. If [op] is [and], then all knowledge in [atl] is added to
% the [knowl] with the tag [n]. If [op] is [or], then the negation
% of all knowledge in [atl] is added to [knowl].
begin scalar at;
while atl do <<
at := car atl;
atl := cdr atl;
knowl := cl_smupdknowl1(op,at,knowl,n);
if knowl eq 'false then <<
atl := nil;
at := 'break
>>
>>;
if at eq 'break then
return 'false
else
return knowl
end;
procedure cl_smupdknowl1(op,at,knowl,n);
begin scalar ent,contra;
if op eq 'or then <<
ent := rl_negateat at;
contra := at
>> else <<
ent := at;
contra := rl_negateat at
>>;
if assoc(contra,knowl) then
return 'false;
if assoc(ent,knowl) then
return knowl;
return knowl := (ent . n) . knowl
end;
procedure cl_smmkatl(op,knowl,newknowl,n);
% Common logic smart simplifier make atomic formula list. [op] is
% one of the operators [and], [or]; [knowl], [newknowl] are
% knowledge bases; [n] is an integer. Returns a list of atomic
% formulas. All knowledge tagged with [n] is extraced from
% [newknowl] and returned as a list of atomic formulas.
begin scalar res;
res := for each pair in newknowl join
if cdr pair = n then {car pair};
if op eq 'or then
res := for each at in res collect rl_negateat at;
return res
end;
procedure cl_smsimpl!-impl(atprem,atconcl,oldknowl,newknowl,n);
% Common logic smart simplifier simplify implication. [atprem] and
% [atconcl] are atomic formulas; [oldknowl] and [newknowl] are
% knowledge bases; [n] is an integer. Returns a formula.
begin scalar w;
w := cl_simpl1(rl_nnf rl_mk2('impl,atprem,atconcl),oldknowl,n,nil);
if rl_tvalp w or cl_atfp w then
return w;
atprem := cl_simpl1(atprem,oldknowl,n,'prem);
atconcl := cl_simpl1(atconcl,oldknowl,n,'concl);
return rl_mk2('impl,atprem,atconcl)
end;
procedure cl_smsimpl!-equiv1(lhs,rhs,oldknowl,newknowl,n);
% Common logic smart simplifier simplify equivalence. [lhs] and
% [rhs] are atomic formulas; [oldknowl] and [newknowl] are
% knowledge bases; [n] is an integer. Returns a formula.
begin scalar w,x;
w := cl_simpl1(rl_nnf rl_mk2('equiv,lhs,rhs),oldknowl,n,nil);
if rl_tvalp w or cl_atfp w then
return w;
x := rl_argn w;
if cl_atfp car x and cl_atfp cadr x and null cddr x then
return w;
lhs := cl_simpl1(lhs,oldknowl,n,'equiv);
rhs := cl_simpl1(rhs,oldknowl,n,'equiv);
if cl_ordp(lhs,rhs) then
return rl_mk2('equiv,lhs,rhs);
return rl_mk2('equiv,rhs,lhs)
end;
procedure cl_siaddatl(atl,c);
% Common logic simplifying add atomic formula list. [atl] is a list
% of atomic formulas; [c] is [true], a simplified atomic formula,
% or a simplified conjunction of atomic formulas. Returns [true],
% [false], a simplified atomic formula, or a simplified conjunction
% of atomic formulas. The result is equivalent to $\bigwedge [atl]
% \land [c]$.
begin scalar w,sicd;
atl := cl_sitheo atl;
if atl eq 'inctheo then
return 'false;
sicd := if c eq 'true then
nil
else if cl_cxfp c then
rl_argn c
else
{c};
w := rl_smupdknowl('and,nconc(atl,sicd),nil,1);
if w eq 'false then
return 'false;
w := rl_smmkatl('and,nil,w,1);
if !*rlsiso then w := sort(w,'rl_ordatp);
return rl_smkn('and,w)
end;
%DS
% <KNOWL> ::= (...,<LAT>,...)
% <LAT> ::= (<ATOMIC FORMULA> . <LABEL>)
% <LABEL> ::= <INTEGER> | ['ignore]
procedure cl_susimkatl(op,knowl,newknowl,n);
% Common logic susi make atomic formula list. [op] is one of the
% operators [and], [or]; [knowl], [newknowl] are KNOWL's; [n] is an
% integer. Returns an list $L$ of atomic formulas. All knowledge
% tagged with [n] is extraced from [newknowl] into $L$.
begin scalar res;
res := for each pair in newknowl join
if cdr pair = n then {car pair};
if null res then return nil;
res := rl_susipost(res,knowl); % TRUE | FALSE | INCTHEO | atl
if rl_tvalp res then
return {cl_cflip(res,op eq 'and)};
if res eq 'inctheo then % Das hatte man auch frueher
return cl_cflip('false,op eq 'and); % wissen koennen.
if op eq 'or then
res := for each at in res collect rl_negateat at;
res := for each at in res collect rl_susitf(at,knowl);
return res
end;
procedure cl_susicpknowl(knowl);
% Common logic susi copy knowledge. [knowl] is a KNOWL. Returns a
% KNOWL. Copies the toplevel and the LAT's of [knowl].
for each p in knowl collect (car p . cdr p);
procedure cl_susiupdknowl(op,atl,knowl,n);
% Common logic susi update knowledge. [op] is one of the operators
% [and], [or]; [atl] is a list of (simplified) atomic formulas;
% [knowl] is a KNOWL; [n] is the current level. Returns a KNOWL.
% Destructively updates [knowl] wrt. the [atl] information.
begin scalar at;
while atl do <<
at := car atl;
atl := cdr atl;
knowl := cl_susiupdknowl1(op,at,knowl,n);
if knowl eq 'false then <<
atl := nil;
at := 'break
>>
>>;
if at eq 'break then
return 'false
else
return knowl
end;
procedure cl_susiupdknowl1(op,at,knowl,n);
% Common logic susi update knowledge subroutine. [op] is one of
% [and], [or]; [at] is a (simplified) atomic formula; [knowl] is a
% KNOWL; [n] is the current level. Returns a KNOWL. Destructively
% updates [knowl] wrt. [at].
if op eq 'and then
cl_susiupdknowl2((at . n),knowl,n)
else % We know [op eq 'or]
cl_susiupdknowl2(((rl_negateat at) . n),knowl,n);
procedure cl_susiupdknowl2(lat,knowl,n);
% Common logic susi update knowledge subroutine. [lat] is a LAT;
% [knowl] is a KNOWL; [n] is the current level. Returns a KNOWL.
% Destructively updates [knowl] wrt. [lat].
begin scalar a,w,sck,ignflg,delflg,addl;
sck := knowl;
while sck do <<
a := car sck;
sck := cdr sck;
w := rl_susibin(a,lat); % 'true | 'false | nil | {commands,...}
if w eq 'false then % What happens with atoms neq false ???
sck := nil
else <<
w := cl_susiinter(w,knowl,a);
addl := nconc(addl,cadr w);
knowl := car w;
if caddr w then
ignflg := T;
if cadddr w then <<
delflg := T;
sck := nil
>>
>>
>>;
if w eq 'false then return 'false;
if null delflg then <<
if ignflg then cdr lat := 'ignore;
knowl := lat . knowl
>>;
while addl do <<
knowl := cl_susiupdknowl2(car addl,knowl,n);
if knowl eq 'false then
addl := nil
else
addl := cdr addl
>>;
return knowl;
end;
procedure cl_susiinter(prg,knowl,a);
% Common logic susi interpreter. [prg] is a SUSIPRG; [knowl] is a
% KNOWL; [a] is a LAT. Returns a list
% $(\kappa,\alpha,\iota,\delta)$, where $\kappa$ and $\alpha$ are
% KNOWL's; $\iota$ and $\delta$ are flags.
begin scalar addl,ignflg,delflg;
for each p in prg do
if car p eq 'delete or car p eq 'ignore then
% if car p eq 'ignore then % We ignore ['ignore]!
% if cdr p then
% ignflg := T
% else
% cdr a := 'ignore
% else if car p eq 'delete then
if cdr p then
delflg := T
else
knowl := delqip(a,knowl)
else if car p eq 'add then
addl := cdr p . addl;
return {knowl,addl,ignflg,delflg}
end;
endmodule; % [clsimpl]
end; % of file