Boost.TypeErasure `any` with a concept returning the same `any`?

Imagine a matrix type, implemented as a B.TE any and a series of structs representing ordinary matrices, etc. It has a set of operations, say, transpose, etc. transpose should return a matrix. Can this be implemented in B.TE? Something like:

BOOST_TYPE_ERASURE_FREE(transpose);

struct ordinary_matrix_impl {};

using matrix =
    any<mpl::vector<copy_constructible<>, has_transpose<matrix(_self&)>>>;

auto transpose(ordinary_matrix_impl&) {
  // ...
  return matrix(ordinary_matrix_impl(/*...*/));
}

But the using matrix = ... doesn't compile (error: 'matrix' was not declared in this scope).

Is there a solution?

Solved it. Just wrap the any in a struct (Compiler Explorer):

#include <boost/mpl/vector.hpp>
#include <boost/type_erasure/any.hpp>
#include <boost/type_erasure/free.hpp>
#include <iostream>

namespace mpl = boost::mpl;
using namespace boost::type_erasure;

BOOST_TYPE_ERASURE_FREE(transpose);

struct ordinary_matrix_impl {};
struct symmetric_matrix_impl {};

struct matrix {
    any<mpl::vector<copy_constructible<>, has_transpose<matrix(_self&)>>> impl;
};

auto transpose(matrix m) {
    return transpose(m.impl);
}

auto transpose(ordinary_matrix_impl& m) {
    std::cout << "make a new ordinary matrix\n";
    return matrix{ordinary_matrix_impl()};
}

auto transpose(symmetric_matrix_impl& m) {
    std::cout << "make a new diagonal matrix\n";
    return matrix{m};
}

auto main() -> int {
    {
        matrix m{ordinary_matrix_impl()};
        auto t = transpose(m);
    }

    {
        matrix m{symmetric_matrix_impl()};
        auto t = transpose(m);
    }

    return 0;
}