rem: memory_iterator<T> operator - ( memory_iterator<T> iter, typename memory_iterator<T>::difference_type  dif ) { iter -= dif; return iter; }
add: ptrdiff_t operator - ( const memory_iterator<T>& other ) const { assert( !( ( raw() - other.raw() )%byte_io::byte_lenght<T>() ) ); return ( raw() - other.raw() )/byte_io::byte_lenght<T>(); }
context: memory_iterator<T> operator - ( memory_iterator<T> iter, typename memory_iterator<T>::difference_type  dif ) {	iter -= dif;	return iter;}