(1) If Cobol is not easy, why is it still used? What is the differences between easy languages and hard languages?

The major reason that Cobol is still widely used in business world is that there are a lot of legacy code written in Cobol during the past thirty years. When Cobol first emerged during the 60’s, some of it’s features well suited the need of writing business software. Although more elegant languages have been designed since then, all the business firms can just discard the legacy code in Cobol, which will cause extra cost and disruption.

(2) How does Gabriel’s theory differ from Hoare and Wirth’s ideas?

The major difference I can see is that Gebriel’s theory is "simplicity centric": easiness to learn, minimum resource requirement, simple performance model and mathematical simplicity. On the other hand, Hoare and Wirth treat simplicity as one of the important means to achieve the ultimate goal: "to help the programer in the practice of his art" (Hoare). So Hoar and Wirth presented more comprehensive ideas for language development.

(3) How does Gobriel’s theory predict that C and C++ will die? What do you actually mean by "better substitution"?

Gobriel did not predict that C will die. On the contrary, he predicts that C has a rather bright future since is fit his simplicity theory very well. Gobriel did predict that the C++ and even the whole object oriented experiment will fail since their performance model is not simple.

What I mean by "better substitution" to Lisp is a language that keep all the good features of Lisp but have simple performance model and have mathematical simplicity for people to lean.