Epsilon: Cannot use "v" or "u"

[theTisch21]

Describe the bug

Typing lowercase "v" or "u" causes a syntax error, even though it should return "undefined" or just a standard variable
I also cannot store a number to either of those as variables
Uppercase "V" or "U" work just fine

Screenshots

To Reproduce

Steps to reproduce the behavior:

1. Go to the 'calculation' app
2. Type 'v' or 'u'
3. Press OK
4. See syntax error
5. Go to the 'functions' app
6. Create a new function
7. Type 'v' or 'u' in the function
8. See syntax error

Expected behavior

I expected it to return "undef" in calculations like any other variable without a value attached to it (see screenshots)
In 'Functions', I expected it to not graph a function, but it instead gives me a syntax error.

Environment

It happens on my N0110 and the online simulator
Simulator: 49b74fb
Calculator: 15.3.0

Note

I first discovered this bug when using the fork Omega, so I originally made an issue there 444 I ended up closing it as it is an epsilon problem, not a problem with Omega.

[RedGl0w]

Indeed, it's somehow duplicate of https://github.com/numworks/epsilon/issues/1622

[artaxxx]

Actually, u and v are reserved for sequences. Just as ln is a reserved named for logarithm. So when you type v(2) you get undef but when you type v it's a syntax error.
I don't know if we can improve this behavior but the main problem here is that the error message isn't enough precise!

[theTisch21]

As it is not a bug, I'm going to close this issue.