This paper is concerned with deterministic ETOL languages. A theorem is proved which, roughly speaking, says that if an ETOL language contains a word which a special property then it must contain an infinite set of words obtained from the given one by “synchronously pumping” a number of subwords of the given word. This theorem has numerous applications for proving that certain languages are not deterministic ETOL languages.
Ehrenfeucht, Andrzej and Rozenberg, Grzegorz, "A Pumping Theorem for EDTOL Languages ; CU-CS-047-74" (1974). Computer Science Technical Reports. 46.