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interface DNode[T] {
var list: seq[T]
invariant
|list| > 0
constructor Init(t: T)
ensures list = [t]
constructor Double(p: T, q: T)
ensures list = [p q]
method List() returns (ret: seq[T])
ensures ret = list
method Size() returns (ret: int)
ensures ret = |list|
method Get(idx: int) returns (ret: T)
requires idx >= 0 && idx < |list|
ensures ret = list[idx]
method Find(n: T) returns (ret: bool)
ensures ret = (n in list)
}
datamodel DNode[T] {
var data: T
var next: DNode[T]
var prev: DNode[T]
frame
next
invariant
next = null ==> list = [data]
next != null ==> (list = [data] + next.list && next.prev = this)
prev != null ==> prev.next = this
}
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