@ARTICLE{AndDasPauSal_j1993, author = {Micea~Andra\c{s}iu and J{\"u}rgen~Dassow and Gheorghe~P\u{a}un and Arto~Salomaa}, title = {Language-theoretic problems arising from {R}ichelieu cryptosystems}, journal = tcs, year = 1993, volume = 116, number = 2, pages = {339--357}, url = {http://dx.doi.org/10.1016/0304-3975(93)90327-P} }