site ThinRing
    references:         Ring
    Ring ThinRing
        abstract        # because we set no values for inner and outer radii
        modelconstraint:OuterRadius <= InnerRadius * 1.10
    ThinRing TenToEleven
        InnerRadius:    10
        OuterRadius:    11
    ThinRing NineToTenIsNotThinEnough
        InnerRadius:    9
        OuterRadius:    10