[28B] \(≤\) is an order relation.
Reflexive property: \(n+0=n\). Antisymmetric property: if \(n+k=m\) and \(m+h=n\) then \(n+k+h=n\) therefore by cancellazione [27V]↺↻ \(h+k=0\), and for [27W]↺↻ \(h=k=0\) so \(n=m\). Transitive property: if \(n+k=m\) and \(m+h=p\) then \(n+k+h=p\).
