EXERCISE 1.3

$\{a,e\}\subset \{x:$$x$ is a vowel in the English alphabet $\}$

$\{1,2,3\}\subset \{1,3,5\}$

$\left\{a\right\}\subset \{a,b,c\}$

$\left\{a\right\}\in \left\{a,b,c\right\}$

$\{x:x$ is an even natural number less than $6\}$ $\subset$ $\{x:x$ is a natural number which divides $36\}$.

Let $A=\{1,2, \{3,4,3,5\}$. Check if the following statement is incorrect or not and justify your answer.

$\{1,2,5\}\in A$

How many elements has $P\left(A\right)$, if $A=\varphi ?$

Write the following as intervals: $\left\{x:x\in R,0\le x<7\right\}$