use strict;
     use AI::Proplog;

     my $p = new AI::Proplog;
     #
     # assert some facts:
     #

     # cs requirements are basic cs, math, advanced cs, an engr rec and nat. sc\
i.
     $p->a( cs_req => qw(basic_cs math_req advanced_cs engr_rec natural_science\
));

     # basic cs requires an intro req, comp org, advanced programming and theor\
y
     $p->a( basic_cs  => qw(intro_req comp_org adv_prog theory) );

     # and so forth
     $p->a( intro_req => 'intro_cs');
     $p->a( intro_req => qw(introI introII) );
     $p->a( math_req  => qw(calc_req finite_req alg_req) );
     $p->a( calc_req  => qw(basic_calc adv_calc) );
     $p->a( basic_calc => qw(calcI calcII) );
     $p->a( basic_calc => qw(calcA calcB calcC) );
     $p->a( adv_calc   => 'lin_alg');
$p->a( adv_calc   => 'honors_linalg');
     $p->a( finite_req => qw(fin_structI stat) );
     $p->a( alg_req    => 'fin_structII');
     $p->a( alg_req    => 'abs_alg');
     $p->a( alg_req    => 'abs_alg');

     # here we assert a bunch of facts:

     # the following things have been taken:
     # cs intro, computer org, advanced programming, and theory
     $p->apl( qw(intro_cs comp_org adv_prog theory) );

     # now do a bottom up search of the fact/rule space to see if the
     # basic cs requirements have been met
     my $R = $p->bottom_up('basic_cs');
    # or:  my $R = $p->top_down('basic_cs');
     ok($R);

##</code><code>##

        $p->a( x => 'y' );
        $p->a( y => 'x' );

##</code><code>##

     # there is a 0.6 chance that a souffle rises is beaten well and it is quie\
t
        $p->a( souffle_rises(0.6) => qw(beaten_well quiet_while_cooking) ) ;

     # there is a 0.1 chance that it will rise based on luck
        $p->a( souffle_rise(0.1 ) => 'have_luck');

     # there is thus 0.3 chance that it will NOT rise

        $p->a( beaten_well(0.4)   => 'use_whisk');
        $p->a( beaten_well(0.6)   => 'use_mixer');

        $p->a( quiet_while_cooking(0.8) => 'kids_outside');
        $p->a( have_luck(0.3) => 'knock_on_wood');

     # tell me what the chances are of this souffle rising if the kids are
     # outside and I use whisk...
        $p->apl( qw(use_whisk kids_outside) );

     $p->top_down('souffle_rise')