\Bibitem{Tho75} \by R.~Thom \paper Topology and linguistics \jour Russian Math. Surveys \yr 1975 \vol 30 \issue 1 \mathnet{http://mi.mathnet.ru//eng/rm4141} \mathscinet{http://mathscinet.ams.org/mathscinet-getitem?mr=495269} \zmath{https://zbmath.org/?q=an:0304.68067}