1 | initial version |

Repeating your input:

```
sage: var('x y')
(x, y)
sage: m = matrix(QQ,[[1,1],[-1,-1],[-1,1]])
sage: ch = ([-1,1,1])
sage: rv = vector([x,y])
sage: k = m.nrows()
sage: u = [(rv-m[i]).norm() for i in range(k)]
```

yields no output, unless we ask for u:

```
sage: u
[sqrt(abs(x - 1)^2 + abs(y - 1)^2),
sqrt(abs(x + 1)^2 + abs(y + 1)^2),
sqrt(abs(x + 1)^2 + abs(y - 1)^2)]
```

Of course, if the definition for `u`

has `.norm`

instead of `.norm()`

,

```
sage: u = [(rv-m[i]).norm for i in range(k)]
```

then we would get:

```
sage: u
[<built-in method norm of Vector_symbolic_dense object at 0x10f76fb48>,
<built-in method norm of Vector_symbolic_dense object at 0x10f76fbb0>,
<built-in method norm of Vector_symbolic_dense object at 0x10f76fc18>]
```

If you are working in the notebook, maybe you evaluated

```
u = [(rv-m[i]).norm for i in range(k)]
```

and *then* changed it to

```
u = [(rv-m[i]).norm() for i in range(k)]
```

but forgot to reevaluate?

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