Hi, Boost.Ratio has a logical submodule providing an extension to the standard see boost::ratio as an MPL type adding struct rational_c_tag : int_<10> {}; This submodule could be moved to the subdirectory of libs/ratio/mpl so that the users of boost::ratio, shouldn't depend on MPL. Boost.Chrono depends already on MPL, but the dependencies are really minor - see below (and can be replaced by StaticAssert and TypeTraits, so that this dependency could be removed also. Do you think removing the dependencies of Boost.Ratio and Boost.Chrono on Boost MPL has value? Best, Vicente P.S. I know that currently TypeTraits depends on MPL, but we expect to resolve this dependency already. |<boost/mpl/assert.hpp>| * from |<boost/chrono/detail/static_assert.hpp>| |<boost/mpl/bool.hpp>| * from |<boost/chrono/detail/static_assert.hpp>| |<boost/mpl/if.hpp>| * from |<boost/chrono/io/duration_get.hpp>| * from |<boost/chrono/io_v1/chrono_io.hpp>| |<boost/mpl/logical.hpp>| * from |<boost/chrono/detail/is_evenly_divisible_by.hpp>| * from |<boost/chrono/duration.hpp>|