The nonnegativity conjecture for cluster variables

Let $\mathcal{A}$ be a cluster algebra of rank $n$ with a seed whose cluster and frozen variables are $x_1,\dots,x_m$. By the Laurent phenomenon, every cluster variable is a Laurent polynomial in the variables $x_1,\dots,x_m$ of any chosen seed. Nonnegativity conjecture. Every coefficient in these Laurent polynomials is nonnegative. This conjecture strengthens the Laurent phenomenon by predicting positivity of the Laurent expansions; the supplied source material does not indicate whether it has been resolved.