src/Isbn.php
public function to10() : Isbn
    {
        if (! $this->is13) {
            return $this;
        }

        return new Isbn(Internal\Converter::convertIsbn13to10($this->isbn), false);
    }
public function to10() : Isbn
    {
        if (! $this->is13) {
            return $this;
        }

        return new Isbn(Internal\Converter::convertIsbn13to10($this->isbn), false);
    }
public function to10 ( ) : Isbn { if ( ! $ this -> is13 ) { return $ this ; } return new Isbn ( Internal \ Converter :: convertIsbn13to10 ( $ this -> isbn ) , false ) ; }
Returns a copy of this Isbn, converted to ISBN-10.

@return Isbn The ISBN-10.

@throws Exception\IsbnNotConvertibleException If this is an ISBN-13 not starting with 978.
Returns a copy of this Isbn converted to ISBN - 10 .