I have several classes with children.
Each child participates in some classes.
I want to know how often participants two children in the same class.
I tried to do with the sumproduct function but I did not really succeed.

For example:

Class A: David,
John, Bob, Ayalon
Class B:
Elijah, Ayalon, Eviatar, Jorge
Class C:
Ayalon, Joshua, David, Elijah
Class D:
Jorge, Bob, Elijah, Eviatar
Class E:
John, Joshua, Bob, David

The expected answer:
name 1: Elijah, name 2:David, answer: 1
name 1: Bob, name 2: John, answer: 2
name 1:
Joshua, name 2: Jorge , answer: 0

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