A set of dictionary matrices and MS rules is said to be WELL-FORMED if, whenever we subject a matrix M to a rule Ri in the course of this process, SD(Ri) is distinct either from M or a sub-matrix of M; i.e. the grammar is well-formed if the SITUATION NEVER ARISES that a matrix M is subjected to a rule Ri where SD(Ri) are incomparable [...]. This well-formedness condition was not given explicitily in Halle [Halle, Morris, 1959, The sound pattern of Russian, The Hague, Mouton] [...].
- Stanley (2004), a pag.66