reference. Circles in synthetic differential geometry [schellingerhout2023circles]

✍️source

@article{schellingerhout2023circles,
 title = {Circles in Synthetic Differential Geometry},
 author = {Schellingerhout, Rob and Portegies, JW},
 year = {2023},
 url = {https://pure.tue.nl/ws/portalfiles/portal/308028780/Thesis_BTW_Rob_Schellingerhout_Report_002_.pdf}
}