12.
What is the purpose of the method_defined? method in Ruby's Module class?

13.
What is an eigenclass in Ruby?

14.
What is the purpose of the include keyword in Ruby?

15.
What does the term "lexical scope" refer to in Ruby?

16.
What is the purpose of the yield keyword in Ruby?

17.
What is the main difference between a lambda and a Proc in Ruby?

19.
What does the term "currying" refer to in Ruby?