##### Exercise1

List four elements of each of the following sets:

\(\{k \in \mathbb{P} \mid {k - 1} \textrm{ is a multiple of 7}\}\)

\(\{x \mid x \textrm{ is a fruit and its skin is normally eaten}\}\)

\(\{x \in \mathbb{Q}\mid \frac{1}{x} \in \mathbb{Z}\}\)

\(\{2n \mid n \in \mathbb{Z}, n < 0 \}\)

\(\{s \mid s = 1 + 2 + \cdots + n \textrm{ for some } n \in \mathbb{P}\}\)