One way to compute the window of a model set (resp. the Rauzy fractal of a tiling) is to consider the ‘lifted’ versions of the expanding maps of the substitution (which are automorphisms of the high dimensional lattice $L$) and their counterparts in the internal space. These are contracting maps yielding an iterated function system. The latter is known to have a unique compact nonempty solution. Multiplying the whole iterated function system by an appropriate factor yields the dual substitution. This was outlined in [Thu89] , see also [Gel97] , [Fre05] . Actually, this is not the only notion of dual tiling. Equivalent concepts in arbitrary dimension are the natural decomposition method [SW02] and - almost sure - the dual substitutions in [SAI01] . In dimension one there are even more equivalent concepts, see for instance [Lam98] .