Chain

Chain rules are a well-known smell in grammar engineering: it happens when a nonterminal is defined with only one production rule which has exactly one nonterminal as its right hand side. The “inner” nonterminal acts like a middle man and does not play a significant rule in structural commitments of the grammar.

Reference

Mats Stijlaart and Vadim Zaytsev. 2017. Towards a taxonomy of grammar smells. In Proceedings of the 10th ACM SIGPLAN International Conference on Software Language Engineering (SLE 2017). ACM, New York, NY, USA, 43-54.