# Question about notation of a Jimbo's paper

I am reading Jimbo's Introduction to Yang-Baxter Equations. And I am confused by the notation he used in the definition:

Here he uses $$u\in C$$ without previously mentioning what is $$C$$. I guess there is some `convention' I missed here. Is $$C$$ the complex field $$\mathbb C$$ (since he takes $$V$$ as a complex vector space), or is it some other Category?

Thanks.

• Complex field. No subtlety, beyond what is about to follow. – Cosmas Zachos May 30 at 0:16