### Pb with unicode character

The following code works perfectly

```
var("w0, pi, D, I")
A = matrix(SR, 2, 2, [[w0, 1],[w0-pi,1]])
y = vector([w0-D, w0-D-pi+I])
sol=A.solve_right(y)
sola=sol[0].full_simplify().function(D, pi, I, w0)
solb=sol[1].full_simplify().function(D, pi, I, w0)
f(x, D, pi, I, w0)=sola*x + solb
show("f(x, D, pi, I, w0)=", f(x, D, pi, I, w0))
```

But if I use \pi <tab> in replacement of pi, there is a Macsyma error