A dense linear order is a chain D = (D, ≤ ) such that ≤ is dense: x < y ⇒ ∃z (x < z and z < y) where x < y ⇔ x ≤ y and x ≠ y.
Let C and D be dense linear orders. A morphism from C to D is a function h : C→D that is a orderpreserving: x ≤ y ⇒ h(x) ≤ h(y).
|Strong amalgamation property|
|Epimorphisms are surjective|