sub Fnnnnnn { 
    my( $a, $b, $c ) = @_; 
    my $x = nnnnnn; 
    return $a * $b - $c; 
}

$f[ nnnnnn ] = sub { 
    my( $a, $b, $c ) = @_; 
    my $x = nnnnnn; 
    return $a * $b - $c; 
}