{% for book in site.data.books-read %} {% assign year_read = book.year_read | times: 0 %} {% if year_read < 2015 %} {% if book.isbn == "None" %} * [{{ book.title }}]({{ book.link }}) by {{ book.author }} (ISBN unknown) {% else %} * [{{ book.title }}]({{ book.link }}) by {{ book.author }} (ISBN: {{ book.isbn }}) {% endif %} {% endif %} {% endfor %}