The Hilbert Curve is one of the earliest FASS-curves. The original algorithm in [hil1891]
bases on one substitution rule and an additional rule which describes how the substitutes have to be connected.
As briefly mentioned in [pau2021]
it is also possible to create the Hilbert Curve by a substitution tiling with two substitution rules and appropriate decorations.
The inflation factor $q$
is 2 and the lines are shifted slightly away from the center of the sides to illustrate the matching rules.
[hil1891]
Hilbert, D
Ueber die stetige Abbildung einer Line auf ein Flaechenstueck
Mathematische Annalen
1891,
38,
459-460,
doi.org/10.1007/BF01199431
[Pau2021]
Pautze, S
Space-Filling, Self-Similar Curves of Regular Pentagons, Heptagons and Other n-Gons
Proceedings of Bridges 2021: Mathematics, Art, Music, Architecture, Culture
2021,
38,
157-164,
bridges2021-157.pdf