I can't. You present me too many restrictions. I could possibly include
In other words, I challenge you to show me one feature of the C++ core language that
1) is not required for C compatibility (such as the struct/class duality),
2) can be simulated with the remaining language features without
2a) significantly increasing source code size or
2b) making the feature inherently more unsafe to use.
The using statement (i.e. using namespace xxx) does not count - I actually think it's useless and tends to lead newbies to bad practices.