Why is this not a regular language So I recently had a problem where I had to create a regular language. After consulting my professor on my solution he told me it was close to correct but to check my definition of a regular language. I am somewhat lost on why my solution is not regular?



From my understanding it meets the requirements of being a right regular language since there is only one non-terminal on the right side of the expression and the non-terminal is the rightmost symbol on the right side of the expression. Are pipe symbols not allowed?
The derivation $T_1 \to U_1$ is not right-regular.  It does not fall into the three allowed categories of rules.  See Wikipedia on right-regular grammars.  If you have a non-terminal on the right-hand side, it needs to be preceded by a terminal.