Getting concrete values from a model containing "array-ext" - z3

Question

When I combine arrays and quantifiers, Z3 often produces models containing applications of array-ext. For example, this test case produces the following model:
(define-fun pipeid () (Array Int Int)
(_ as-array k!2))
(define-fun valid () (Array Int Bool)
(_ as-array k!0))
(define-fun ispipe () (Array Int Bool)
(_ as-array k!1))
(define-fun pipeid_ab () Int
2)
(define-fun fd () Int
0)
(define-fun k!3 ((x!1 Int)) Int
(ite (= x!1 0) 0
(array-ext (_ as-array k!0) (_ as-array k!1))))
(define-fun k!0!4 ((x!1 Int)) Bool
(ite (= x!1 3) false
true))
(define-fun k!0 ((x!1 Int)) Bool
(k!0!4 (k!3 x!1)))
(define-fun k!1 ((x!1 Int)) Bool
true)
(define-fun k!2!5 ((x!1 Int)) Int
(ite (= x!1 3) 4
1))
(define-fun k!2 ((x!1 Int)) Int
(k!2!5 (k!3 x!1)))
First, what does the array-ext in k!3 mean? I've pieced together that (array-ext a b) is some index x for which a[x] != b[x], but either what I've pieced together is incorrect or I can't wrap my head around the circular definitions of k!0 and k!3 above.
Second, how can I extract concrete values from such models? I know that it's not in general possible to represent the concrete value of an array directly in the model, but I would like to at least understand what its concrete value is and be able to extract it in some form from the model. Even querying for individual array indices doesn't seem to help:
model.evaluate(pipeid[1]) => If(array-ext(as-array, as-array) = 3, 4, 1)
Thanks.

Answer 1

array-ext is an internal function symbol. It is used to implement array extensionality.
That being said, it should not appear in models. The model-based-quantifier-instantiation (MBQI) module accidentally "leaks" the array-ext into the model. I fixed the problem.
http://z3.codeplex.com/SourceControl/changeset/185f125f7a3d356192df272bfb2339ad36d3cdf9
The fix is already available in the unstable (work-in-progress) branch.
It will also be available in the nightly builds.
Here is the output after the bug fix:
(define-fun pipeid () (Array Int Int)
(_ as-array k!2))
(define-fun valid () (Array Int Bool)
(_ as-array k!0))
(define-fun ispipe () (Array Int Bool)
(_ as-array k!1))
(define-fun pipeid_ab () Int
2)
(define-fun fd () Int
0)
(define-fun k!3 ((x!1 Int)) Int
0)
(define-fun k!0!4 ((x!1 Int)) Bool
(ite (= x!1 3) false
true))
(define-fun k!0 ((x!1 Int)) Bool
(k!0!4 (k!3 x!1)))
(define-fun k!1 ((x!1 Int)) Bool
true)
(define-fun k!2!5 ((x!1 Int)) Int
(ite (= x!1 3) 4
1))
(define-fun k!2 ((x!1 Int)) Int
(k!2!5 (k!3 x!1)))
pipeid[0] => 1
pipeid[1] => 1