z yields a finite sentence, a fixed point of the procedure of finding all the instances of that letter and enumerating their positions. Some find non-trivial fixed points, like
'f' is the first and seventh letter of this sentence.
My procedure for 'l' remains finite but finds no fixed point, switching between
'l' is the first and twenty-eighth letter in this sentence
'l' is the first and twenty-seventh letter in this sentence
neither of which is true. 'c' cycles through (1st, 20th and 56th), (1st, 52nd), (1st, 22nd, 44th), none of which are true.
Others diverge, like 'n' and 'e'
'e' is the first, sixth, [... no fixed point found ...]
where the tail of the sentence just explodes on every iteration. What happens is also sensitive to the [presumed] end of the sentence 'letter in this sentence'.
The most interesting one is 'r', which doesn't explode in length after 100 iterations but (if it loops, which I haven't established) has a very long period.
I also found a few fixed points like
'a' is the first and twelfth letter of this sentence
which doesn't come from iterating on "'a' is the first letter of this sentence"; I think it's an Eden.
Others diverge, like 'n' and 'e'
where the tail of the sentence just explodes on every iteration. What happens is also sensitive to the [presumed] end of the sentence 'letter in this sentence'.The most interesting one is 'r', which doesn't explode in length after 100 iterations but (if it loops, which I haven't established) has a very long period.
I also found a few fixed points like
which doesn't come from iterating on "'a' is the first letter of this sentence"; I think it's an Eden.