# Time-varying grammar with period 2:  V1 = { S -> aT },  V2 = { T -> bS, T -> b }.   L = { (ab)^n : n >= 1 }
# At steps 1, 3, 5 ... the rules of V1 apply, at steps 2, 4 ... those of V2: one component per rule set,
# each pointing to the next.

# the words of the language: a string of terminal symbols (lower-case letters) that reaches component 3 is marked
[model.components.3.marks]
terminal = '\A[a-z]*\Z'

[axioms]
1 = ["S"]

[rules.1]
# rule set V1 (steps 1, 3, 5 ...): S -> aT, then V2 applies
S -> a T, 2
[rules.2]
# rule set V2 (steps 2, 4 ...): T -> bS goes back to V1 ...
T -> b S, 1
# ... or T -> b finishes the word in component 3
T -> b, 3
