Hello!
I have found mistake in documentation on version 7.2. Tutorial.
[tutorial-7.2-A4.pdf]
In chapter 3.3 (Foreign Keys) i have found the next mistake:

CREATE TABLE weather (
city varchar(80) references weather,
.....
);

There must be next string:

city varchar(80) references cities,

Sorry for bad English :)

Good Luck!

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