“…An alternative approach to reach low temperatures and long times, but without a microscopic foundation, is to study simple models of glassiness, kinetically constrained models (KCMs) [19,20,21,22,23,24], such as the Fredrickson-Andersen (FA) model [20] or the East model [25], or variations such as the North-East model [23], which mimic the constrained dynamics of real glassy systems but have trivial thermodynamics. These may be viewed as effective models for glasses, in terms of some coarse-grained degree of freedom often labelled "spins", also termed a "mobility field" by some authors [23].…”