UML22 — section 2.10.4.1 detailed semantics of collaborations

My question concerns section 2.10.4.1 (detailed semantics of collaborations). The last part of the 4th paragraph starts as follows:

"However, instances of different classifiers can play the role defined by the classifier role, as long as they have all the required properties."

Allow me to illustrate my interpretation of this section by means of an example.

Suppose there is a class A with 5 operations, o1, o2, o3, o4 and o5, and there is a class B with 3 operations, identical to o2, o3 and o4.
Suppose there is a classifier role R in a collaboration, which has A as its base. The role can then specify a subset of the features of A. These features are then required by instances which play the role. Suppose this subset consists of o2 and o3. Then the quote from the spec above claims that instances of B are allowed to play role R. Is this correct so far?

Then, the spec goes on:

"Several classifier roles may have the same base classifier, even in the same collaboration, but their features and contained elements may be different subsets of the features and contained elements of the classifier. These classifier roles specify different roles played by (possibly different) instances of the same classifier."

So, considering again role R from my example, suppose there is now a different classifier role Q, which also has A as its base. Suppose Q specifies o3 and o4 as the required subset of A's features.

Now the last sentence from the spec quote seems to say that only (possibly different) instances of A can play roles R and Q. This would mean that an instance of B is NOT allowed to play either R or Q, which would contradict my example above.

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