Function backward_link 

pub fn backward_link(th: Rc<DiscreteTabTheory>) -> DiscreteTabModel

The “walking” backward link.

This is the free category with links that has a link from the codomain of a morphism back to the morphism itself.

In system dynamics jargon, a backward link defines a “reinforcing loop,” assuming the link has a positive effect on the flow. An example is an infection flow an infectious disease model, where increasing the number of infectives increases the rate of infection of the remaining susceptibles (other things equal).