“…Since then many researchers have studied the corresponding structures for other substitutions, with quite diverse outcomes (cf. [2,5,41,47,16,4,20,45,26,21,48]), but a general rule for deciding when a substitution leads to simple tiling of a space is still wanted, especially, because these structures turned out to be useful in the mathematical theory of quasicrystals (for details see [44,7,27,10]). …”