I thought I'd add: what's the "mono" in "monoid"? It's that the ports come in only one compatibility type. For example, devices that have exactly two ports, o

I thought I'd add: what's the "mono" in "monoid"? It's that the ports come in only one compatibility type. For example, devices that have exactly two ports, one male and one female, for some type of connector, maybe USB-A. If you plug one into another, then you have a new device with the same properties, at least as far as ports are concerned.