Whereas in IIT 3.x the distance function is an adaptation of the KL-divergence over probability distributiosn (cf. Kleiner & Tull for details), IIT introduces a new distance measure, called '''Intrinsic Difference'''.
<!-- Add definition, possibly
;Def. Intrinsic Difference
: TBA
-->
For details and a justification of it, cf. Barbosa et al., A measure for intrinsic information, 2020.
== More constrained partitions ==
In IIT 3.x, every choice of subsystems gave a partition of the system. In IIT 4.0, partitions are more constrained, they have to destroy the mechanism.
== Introduction of Relations ==