UML14 — OCL Error

sUnique for Collections is defined as follows:
>>
>>collection->isUnique(expr : OclExpression) : Boolean
>> post: result = collection->collect(expr)->forAll(e1,e2 | e1<>e2)
>>
>>Unfortunately, if the collection is not empty, this expression
>>always evaluates to false. This is due to the fact that in a
>>forAll over two iterators, both iterate over the full collection.
>>Therefor, for each element in the collectionen , there is a
>>step where both itereters point to this element, but at this
>>point, e1 <> e2 evaluates to false.
>>
>>My suggestion for the definition of isUnique would be as follows:
>>
>>collection->isUnique(expr : OclExpression) : Boolean
>> post:
>> let res = collection->collect(expr) in
>> result = res->forAll(e $|$ res->count(e) = 1)
>>
>>This expression states, that each element in the collection 'res'
>>appears exactly once, i.e. is unique.

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