And my favorite one may be or at least the one I learned about most recently, is even the idea of supporting recursion of letting a function call itself, most languages ha ve supported this for a long, long time, but back in the 1960s, it was a very controversial idea, of whether your language should have to support this, and of course, even more recently people love to pick on old versions before trend, it was not something that could be conveniently done in certain languages. 