Matthias Jantzen.
The power of synchronizing operations on strings.
Theoretical Computer Science, 14:127-154, 1981.
@article{Jantzen81e,
Author = {Jantzen, Matthias},
Journal = TCS,
Pages = {127--154},
Title = {The power of synchronizing operations on strings},
Volume = 14,
Year = 1981
}