The main header you will always need to use Boost.YAP is the <boost/yap/algorithm.hpp> header. If you want to ensure that you don't accidentally use expression<> (which I recommend), just include this header and nothing else.

If you want to use the expression<> reference expression template (great for prototyping, but not recommended for production work), include the <boost/yap/expression.hpp> header.

If you want to include all of the above, use the <boost/yap/yap.hpp> header.

If you want to use print(), include the <boost/yap/print.hpp> header; this header is not included in the <boost/yap/yap.hpp> header.