Some logical functors to build more complex queries:

True and False. No supprise, they always return true or false.
Not<TCondition>. TCondition is a functor, and its result is inverted.
Chain<TACondition,TBCondition>. TACondition and TBCondition are functors, and Chain evaluates TACondition && TBCondition.

As it's no fun to get and write the correct template arguments, convenience functions creating the correct functor are provided.

true_c and false_c. (provided just to match the schema)
not_c. Takes a functor as argument and returns the appropriate Not functor.
chain. Takes two functors and returns the appropriate Cain functor.

struct Print; // functor printing elements
struct Count; // functor counting number of elements
 
std::for_each( c.begin(), c.end(),
               chain( Print(), Count() ) );