public function isShared( $abstract )
    {
        if ( isset( $this->bindings[ $abstract ][ 'shared' ] ) )
        {
            $shared = $this->bindings[ $abstract ][ 'shared' ];
        }
        else
        {
            $shared = FALSE;
        }

        return isset( $this->instances[ $abstract ] ) || TRUE === $shared;
    }