Add corollary extension

[Oleg Endo]

On Thu, 2012-06-28 at 18:08 -0400, Rick C. Hodgin wrote:
> How would you handle:
> 
> isSystemClosed = true;

By adding one line to inv_bool....

struct inv_bool {
   bool& b;
   operator bool() const { return !b; }
   inv_bool& operator = (bool _b) { b = !_b; return *this; }
};


Cheers,
Oleg