A partial order is an antisymmetric preorder, i.e. a binary relation that is reflexive, transitive and antisymmetric.
A strict partial order is a binary relation that is irreflexive, transitive and asymmetric.
A relation is a strict partial order as soon as it is irreflexive and transitive.
Proof.By PROP-RCL-ITA.
$\preceq$ is a partial order if and only if $\prec$ is a strict partial order.