«Left 4 Dead 2 Interview». eurogamer.net. 3 de julio de 2009. Consultado el 5 de julio de 2009. «The AI director—I don't want to say it fell out of Half-Life 2, but it was definitely a jumping-off point of stuff we did in Half-Life 2, particularly Episode 2. There are a couple of key battles where the number of Combine, and where they come at you from, uses something like that. It's much cruder than what we accomplished with Left 4 Dead, but there was some of that there».
