Unextendibility of Mutually Unbiased Bases

Besides being of independent interest in understanding the structure of (partial) MUB collections and their conjugacy classes, satisfactory answers to these questions will help the following investigations: – the search for lower bounds on the number of MUBs and specifically for efficient constructions; – the search for upper bounds on the number of MUBs even for small non-prime-power dimensions, either using automated refutation methods, or using computer programs that exhaustively generate all (conjugacy classes of) MUB collections.