use AI::Perlog;
my $pg = AI::Perlog->new;
$pg->add_fact( gives => qw/ Ovid money kudra / );
$pg->add_fact( gives => qw/ grep grief Ovid / );

# an underscore is synonymous with the empty string or undef
print "y\n" if $pg->gives( qw/ _ _ kudra / );       # does anyone give anything to kudra?
print "y\n" if $pg->gives( '', '', 'kudra' );       # same thing
print "y\n" if $pg->gives( undef, undef, 'kudra' ); # same thing
print "y\n" if $pg->gives( qw/ grep _ Ovid / );     # does grep give anything to Ovid?
print "n\n" if ! $pg->gives( qw/ Ovid _ grep / );   # Returns false. Ovid gives nothing to grep