BPMN11 — Why in paragraph 7.1.1 Uses of BPMN, definition of Collaboration (Global)

I am beginner in BPM but in order to understand the BPMN standard, I send these questions: 1) Why in paragraph 7.1.1 Uses of BPMN, the definition of Collaboration (Global) Process (page 14) says: The collaboration process can be shown as two or more abstract process communicating with each other (see figure 7.3).... But the Figure 7.3 looks like as "two or more private (internal) business processes communicating with each other", comparing the Figure 7.1 and Figure 7.2 For more emphasis what I saying In the Figure 7.3 both process (patient and Receptionist/Doctor), all activities for both process are shown, this is not agree with definition of Abstract (public) process (page 13), that says: ....All other "internal" activities of the private business process are not shown in the abstract process.... 2) if the difference between Private (internal) business processes and Collaboration (Global) processes is the number of business entities, this mean that : Private (internal) business processes for only one business entity or specific organization. Collaboration (Global) processes for two or more business entities. What about Abstract (Public) processes, how many entities are or can be involved? 3) The Abstract (public) Processes are "abstract" because the activities of the another process or participant are not shown ?, using words of the definition of the Abstract (public) Processes.