Upper and Lower Cortex

[shawntanzk]

It would be useful to have upper and deep layers as defined by https://www.biorxiv.org/content/10.1101/2022.10.12.511898v1.full.pdf

Although cortical layers two through four are
commonly considered “upper” and layers five and six
“deep,” both upper-layer IT and deep-layer IT superclusters 
contained putative Layer-4 clusters 

Axiomatization with layer 4 might be tricky?
Perhaps doing it like mix cortical layers that do not have logical axioms would make sense

[shawntanzk]

Related to obophenotype/cell-ontology#1743