Published online by Cambridge University Press: 20 November 2018
If $\mathfrak{A}$ is a finite alphabet,
$\mathcal{U}\,\subset \,{{\mathbb{Z}}^{D}}$, and
${{\mu }_{\mathcal{U}}}$ is a probability measure on
${{\mathfrak{A}}^{\mathcal{U}}}$ that “looks like” the marginal projection of a stationary stochastic process on
${{\mathfrak{A}}^{{{\mathbb{Z}}^{D}}}}$, then can we “extend”
${{\mu }_{\mathcal{U}}}$ to such a process? Under what conditions can we make this extension ergodic, (quasi)periodic, or (weakly) mixing? After surveying classical work on this problem when
$D\,=\,1$, we provide some sufficient conditions and some necessary conditions for
${{\mu }_{\mathcal{U}}}$ to be extendible for
$D\,>\,1$, and show that, in general, the problem is not formally decidable.