1. Homo Ludens: A Study of Play-Element in Culture;Huizinga,1998
2. Man, Play, and Games;Caillois,2001
3. Fun Inc: Why Games Are the Twenty-First Century’s Most Serious Business;Chatfield,2010
4. Gaming Market—Growth, Trends, Forecasts (2020–2025)
https://www.researchandmarkets.com/reports/4845961/gaming-market-growth-trends-forecasts-2020