1 | initial version |

Use the chart method `add_restrictions`

(type `X.add_restrictions?`

for the documentation).
On your example, this gives:

```
sage: M = Manifold(4, 'M', latex_name=r'\mathcal{M}', structure='Lorentzian')
sage: X.<t,r,th,ph> = M.chart(r"t r:(0,+inf) th:(0,pi):\theta ph:(0,2*pi):periodic\phi")
sage: X.add_restrictions(r < th^2+0.52)
```

The condition `r < th^2 + 0.52`

is not shown by `X.coord_range()`

(maybe it should?), but one can check that it has been taken into account:

```
sage: X.valid_coordinates(0, 1, pi/2, pi)
True
sage: X.valid_coordinates(0, 4, pi/2, pi)
False
sage: p = M((0, 4, pi/2, pi))
ValueError Traceback (most recent call last)
...
ValueError: the coordinates (0, 4, 1/2*pi, pi) are not valid on the Chart (M, (t, r, th, ph))
```

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