Intrinsic form the essential interface of every Fusion Sequence. STL counterparts of these functions are usually implemented as member functions. Intrinsic functions, unlike Algorithms, are not generic across the full Sequence repertoire. They need to be implemented for each Fusion Sequence  .
#include <boost/fusion/sequence/intrinsic.hpp> #include <boost/fusion/include/intrinsic.hpp>
 In practice, many of intrinsic functions have default implementations that will work in majority of cases