(*#* **Examples of semi-groups: $\langle$#⟨#[Z],[[+]]$\rangle$#⟩# and $\langle$#⟨#[Z],[[*]]$\rangle$#⟩#
***$\langle$#⟨#[Z],[[+]]$\rangle$#⟩#
*)
(*#* **Examples of semi-groups: $\langle$#⟨#[Z],[[+]]$\rangle$#⟩# and $\langle$#⟨#[Z],[[*]]$\rangle$#⟩#
***$\langle$#⟨#[Z],[[+]]$\rangle$#⟩#
*)