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The Grassl-Rötteler cyclic and consta-cyclic MDS codes are generalised Reed-Solomon codes

We prove that the cyclic and constacyclic codes constructed by Grassl and Rötteler in arXiv:1502.05267 are generalised Reed-Solomon codes. This note can be considered as an addendum to that article. It can also be considered as an appendix to arXiv:2106.10180, where Conjecture 11 of arXiv:1502.0526, which was stated for Grassl-Rötteler codes, is proven for generalised Reed-Solomon codes. The content of this note, together with arXiv:2106.10180, therefore implies that Conjecture 11 from arXiv:1502.0526 is true.