### Another problem simplifying symbolic trigonometric expressions

I am testing Sage with the notebook interface, and I want to simplify this trigonometric symbolic expression:

```
var('x1','x2')
exp1=sin(x1)*cos(x2)+sin(x2)*cos(x1)
print(exp1.trig_simplify())
```

Sage does not simplify this expression and the result is:

```
cos(x2)*sin(x1) + cos(x1)*sin(x2)
```

As you can see the result show be:

```
sin(x1+x2)
```

Is there any to simplify trigonometric functions applied to the addition or the subtraction of two values?
Thanks