Dear All, I'm trying to do some simple tests with the proposed Heaps library, but I get a mountain of compiler errors that start like this: ./boost_heap-HEAD-449f378/boost/heap/priority_queue.hpp:32: error: ‘optional’ was not declared in this scope ./boost_heap-HEAD-449f378/boost/heap/priority_queue.hpp:32: error: template argument 1 is invalid ./boost_heap-HEAD-449f378/boost/heap/priority_queue.hpp:32: error: expected unqualified-id before ‘,’ token I thought this was probably due to me having a too-old boost installation, but I believe I'm now compiling with 1.46.1 and I get the same error (though I need to verify that my paths are all set correctly). Any ideas anyone? (I've arrived late to this review having been away, but I'd like to do some quick benchmarks if I have time.) Thanks, Phil.