For the notation convenience and consistancy, throughout this paper, we show terminals and non-terminals by lowercase and uppercase letters, respectively and sets and multisets by bold font uppercase letters.
using the rules in (6) a sentence of the language (which is a multiset in this model) can be derived as follows: Once the set is generated, it can be realized as any of the six permutation of d, e, and c. a single sequence of derivations can lead to six different strings of words.