Suppose for a moment that the chinese dominate the world (there are few people who believes in this idea..).
Suppose you, if they wants to aply a birth control worldwide, people must fulfills this law: every family can have only one child.
And then, with this law,...which (family) relationships disappear?
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Solution:
With this law, a lot of relationships disappear: brother, sister, aunt, uncle, cousins, brother-in-law, sister-in-law, etc