A k-grammar is yet another kind of parallel grammar, very different from an Indian parallel grammar, but still with a level of parallelism. In a k-grammar, for some number "k", exactly "k" non-terminal symbols must be rewritten at every step (except the first step, where the only symbol in the string is the start symbol). If the string has less than "k" non-terminals, the derivation fails. A 3-grammar can produce the language formula_201, as can be seen below:  Let formula_202, where "P" consists of:  With the following derivation for "":  At each step in the derivation except the first and last, we used the self-recursive rules formula_211. If we had not use the recursive rules, instead using, say, formula_212, where one of the rules is not self-recursive, the number of non-terminals would have decreased to 2, thus making the string unable to be derived further because it would have too few non-terminals to be rewritten. Russian parallel grammars are somewhere between Indian parallel grammars and k-grammars, defined as formula_213, where "N", "T", and "S" are as in a context-free grammar, and "P" is a set of pairs formula_214, where formula_215 is a context-free production rule, and "k" is either 1 or 2. Application of a rule formula_216 involves rewriting "k" occurrences of "A" to "w" simultaneously. A scattered context grammar is a 4-tuple formula_1 where "N", "T", and "S" are defined as in a context-free grammar, and "P" is a set of tuples called matrixes formula_218, where formula_219 can vary according to the matrix. The derives relation for such a grammar is  Intuitively, then, the matrixes in a scattered context grammar provide a list of rules which must each be applied to non-terminals in a string, where those non-terminals appear in the same linear order as the rules that rewrite them. An unordered scattered context grammar is a scattered context grammar in which, for every rule in "P", each of its permutations is also in "P". As such, a rule and its permutations can instead be represented as a set rather than as tuples. Scattered context grammars are capable of describing the language formula_201 quite easily.