How to bound variable?

[olugovoy]

Hello,

I have two general questions:

1. Does Dynare solve models with inequalities?
I need bound a variable in my model in interval [0,1]. Few others vars I have to make positive.
I tryed:
model;
mu>=0;
mu<=1;
...
But it doesn't work.
How can I bound variables in Dynare?

2. May I determine exogenous variables within Dynare code?
I'm trying to put an equation for exogenous variable 'a' :
model;
a = 0.9*a(-1);
...
but it results error: "exogenous variable has lag...".

Thanks,
Oleg