Zend Technologies & Herbert, S. (2005). Zend PHP certification study guide. Sams Pub..
Lua i Stíl Chicago (17ú heag.)Zend Technologies agus Stuart Herbert. Zend PHP Certification Study Guide. Indianapolis, Ind: Sams Pub., 2005.
Lua MLA (8ú heag.)Zend Technologies agus Stuart Herbert. Zend PHP Certification Study Guide. Sams Pub., 2005.
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