|| x ||,

Now for s, t IRk, a weakly harmonizable spatially isotropic covariance r(s, t, •, •) belongs to Gn defined earlier.

By using the definition of Gn as the class of all n-dimensional harmonizable isotropic covariance functions, some basic stability properties of a weakly harmonizable spatially isotropic covariance from Gn may be deduced. Proposition 1. i) If r(s,t, •,•) belongs to Gn and a, b are two arbitrary positive constants, then a(r(bs,bt, •,•)) belongs to Gn .