public function previousX()
    {
        if ($this->previousXExists()) {
            $this->seekX($this->keyX()-1);
        } else {
            $this->x = null;
        }
        return $this;
    }
public function previousX()
    {
        if ($this->previousXExists()) {
            $this->seekX($this->keyX()-1);
        } else {
            $this->x = null;
        }
        return $this;
    }
public function previousX ( ) { if ( $ this -> previousXExists ( ) ) { $ this -> seekX ( $ this -> keyX ( ) - 1 ) ; } else { $ this -> x = null ; } return $ this ; }
Seek to current `x` less 1

@return  $this
Seek to current x less 1