3
我有两个关于Z3如何操作数组的问题。关于Z3中数组的限制
1)在模型中,数组有一个“else”元素以及相应的值。有没有一种方法来指定公式中数组上“else”元素的约束?例如,我们可以指定数组的第一个元素大于5,而其他所有元素都小于5?
2)当在命令行经由Z3检查下列公式,
(set-logic QF_AX)
(declare-sort Index 0)
(declare-sort Element 0)
(declare-fun a1() (Array Index Element))
(declare-fun i0() Index)
(declare-fun i1() Index)
(assert
(let
(
(?v_1 (select a1 i0))
(?v_2 (select a1 i1))
)
(
not(= ?v_1 ?v_2)
)
)
)
Z3产生如下的输出。
sat
(model
;; universe for Index:
;; Index!val!1 Index!val!0
;; -----------
;; definitions for universe elements:
(declare-fun Index!val!1() Index)
(declare-fun Index!val!0() Index)
;; cardinality constraint:
(forall ((x Index)) (or (= x Index!val!1) (= x Index!val!0)))
;; -----------
;; universe for Element:
;; Element!val!1 Element!val!0
;; -----------
;; definitions for universe elements:
(declare-fun Element!val!1() Element)
(declare-fun Element!val!0() Element)
;; cardinality constraint:
(forall ((x Element)) (or (= x Element!val!1) (= x Element!val!0)))
;; -----------
(define-fun i1() Index
Index!val!1)
(define-fun a1() (Array Index Element)
(_ as-array k!0))
(define-fun i0() Index
Index!val!0)
(define-fun k!0 ((x!1 Index)) Element
(ite (= x!1 Index!val!0) Element!val!0
(ite (= x!1 Index!val!1) Element!val!1
Element!val!0)))
)
在通过Z3py检查相同的公式时,会生成以下模型。
[i1 = Index!val!1,
a1 = [Index!val!0 -> Element!val!0,
Index!val!1 -> Element!val!1,
else -> Element!val!0],
i0 = Index!val!0,
k!0 = [Index!val!0 -> Element!val!0,
Index!val!1 -> Element!val!1,
else -> Element!val!0]]
有趣的是,在a1
提及k!0
在Z3py “引用”,即,a1
指FuncInterp
对象。情况总是如此吗?特别是,如果一个程序在Z3py提供的模型上行走,假设所有的as_array
表达式都将被解析为底层函数定义是否安全?