# arctan of infinity is undefined

Using the following code for an equation, I get an undefined result for `arctan(oo)`

:

```
sage: var('t, p, w')
(t, p, w)
sage: a = w^2
sage: b = w
sage: k = b/a
sage: phi = arctan(k)
sage: a = lim(k, w=0)
sage: a
Infinity
sage: lim(phi, w=0) # should be pi/2 ?
und
sage: b = oo
sage: arctan(b)
1/2*pi
sage: a==b
True
sage: arctan(a)
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
...
TypeError: cannot coerce arguments: no canonical coercion from The Unsigned Infinity Ring to Symbolic Ring
```

What is wrong?