# Stringification of concatenate expressions

I am not sure for the title of this question

This code

```
nl=3
nc=2
ring=QQ
A=matrix(ring,nl,nc,[3,2,1,4,1,1])
b=vector(ring,[3,5,6])
# b=random_vector(ring,nc)
c=vector(ring,[4,7])
sign=list([">=",">=","<="])
vsign=list([">=",">="])
Zer =[0 for v in vsign]
x = var("x_", n=nc)
L=list(zip(zip(x,vsign),Zer))
LL=[flatten(v) for v in L]
LL
```

produce this `[[x_0, '>=', 0], [x_1, '>=', 0]]`

. I would like to obtain `[['x_0 >= 0'], ['x_1 >= 0']]`

. If I transform early all the `x_i`

in string I can obtain easily `[['x-0 >= 0'], ['x-1 >= 0']]`

. I wonder why 'stringify' transform `-`

to `_`

.

What is

`stringify`

? The built-in function`str`

doesn't convert`_`

to`-`

.