sub functional_unglue {
    my %x = @_;
    my $x = $x{target};     
    my $l = $x{lexicon};    
    my $f = $x{pre_images}; 
    my @q = ([$x]);
    my @r;
    while(@q){
        my $t = shift @q;
        my @w = @{$t};
        my $w = pop @w;
        for(keys %$f){
            if(my @y = $f->{$_}->($w,$l,$f)){
                result:
                for my $i(0..$#y){        
                    my $n = $#{$y[$i]} == 0 ? 0 : $#{$y[$i]} - 1;
                    for my $j(0..$n){
                        next result unless exists $l->{$y[$i][$j]}
                    }
                    push @q, [@w,@{$y[$i]}]
                }
            }
        }
        if(exists $l->{$t->[$#{$t}]}){
            push @r, $t
        } 
    } @r
}