(*#* **Example of a semi-group: $\langle$#⟨#[Qpos],$(x,y) \mapsto xy/2$#(x,y) ↦ xy/2#$\rangle$#⟩#
The positive rationals form with the operation
$(x,y) \mapsto xy/2$#(x,y) ↦ xy/2# a CSemiGroup.
*)
(*#* **Example of a semi-group: $\langle$#⟨#[Qpos],$(x,y) \mapsto xy/2$#(x,y) ↦ xy/2#$\rangle$#⟩#
The positive rationals form with the operation
$(x,y) \mapsto xy/2$#(x,y) ↦ xy/2# a CSemiGroup.
*)