Diamond

A well-known pattern in dependency and inclusion is when a class A inherits from class X and class B also inherits from class X, but class C inherits from both A and B and thus gets to see double of each of X’s elements. The problem is solved differently in different programming and modelling languages—in grammars, it causes an ambiguity.

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.