Saudi, Mohd Haizam Mohd, Obsatar Sinaga, Djoko Roespinoedji, and Mohd Shahril Ahmad Razimi. 2019. “Environmental Sustainability in the Fourth Industrial Revolution: The Nexus Between Green Product and Green Process Innovation”. International Journal of Energy Economics and Policy 9 (5):363-70. https://econjournals.com.tr/index.php/ijeep/article/view/8281.