Question:
Let $A=\{\phi,\{\phi\}, 1,\{1, \phi\}, 2\}$. Which of the following are true?
(i) $\phi \in A$
(ii) $\{\phi\} \in A$
(iii) $\{1\} \in A$
(iv) $\{2, \phi\} \subset A$
(v) $2 \subset A$
(vi) $\{2\{1\}\} \not \subset A$
(vii) $\{\{2\},\{1\}\} \not \subset A$
(viii) $\{\phi,\{\phi\},\{1, \phi\}\} \subset A$
(ix) $\{\{\phi\}\} \subset A$
Solution:
(i) True
(ii) True
(iii) False
The correct form would be $\{1\} \subset A$.
(iv) True
(v) False
The correct form would be $1 \in A$.
(vi) True
(vii) True
(viii) True
(ix) True