After my Heston remark on stochastic volatility

https://papers.ssrn.com/sol3/papers.cfm ... id=3046261

the idea to look more thoroughly the Black Scholes option derivation did lead me to a critical point to their derivation. It presented at

https://www.slideshare.net/secret/K20W7nhXBcTKJs

https://papers.ssrn.com/sol3/papers.cfm ... id=3049495

Your critical comments are welcome.