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1. Phrases that must be true

2. Sentences "A" and "B" are entailed

   • The so called A-B test
     • It might be redundant
       • Peter has a son and his son is handsome
         • A entails B
         • Peter does not have a son and he is handsome
           • A does not entail B

3. Both are either true or false

4. Despite extra noun phrases, the main idea remains

   • John is an amateur teacher. John is a professional teacher.
     • Both remain that John is a teacher.

5. Contradiction occurs when

   • They are not the same
     • John is a guitar player
     • John can't stand playing instruments