(*#* **Examples of semi-groups: $\langle$#⟨#[Npos],[[+]]$\rangle$#⟩# and $\langle$#⟨#[Npos],[[*]]$\rangle$#⟩#
***$\langle$#⟨#[Npos],[[+]]$\rangle$#⟩#
(*#* **Examples of semi-groups: $\langle$#⟨#[Npos],[[+]]$\rangle$#⟩# and $\langle$#⟨#[Npos],[[*]]$\rangle$#⟩#
***$\langle$#⟨#[Npos],[[+]]$\rangle$#⟩#
(*#* ***$\langle$#⟨#[Npos],[[*]]$\rangle$#⟩#
Also together with multiplication, the positive numbers form a semigroup.
*)
(*#* ***$\langle$#⟨#[Npos],[[*]]$\rangle$#⟩#
Also together with multiplication, the positive numbers form a semigroup.
*)