The Rado-minor conjecture for M-natural-concave valuations

Let $v:2^{\mathcal G}\to\mathbb R$ be a valuation. An endowment operation with respect to $T\subseteq\mathcal G$ produces the valuation $v'(X)=v(X\cup T)-v(T)$, and a Rado minor valuation is one obtained from a Rado valuation by such an operation. An $M^\natural$-concave valuation is a valuation in the discrete-concavity class denoted by $M^\natural$-concavity. Rado-minor conjecture. Every $M^\natural$-concave valuation arises as a Rado minor valuation. Rado valuations are not closed under endowment, whereas the conjectured minor class is; the source states that this conjecture is still open.