Also if you, dear reader, have suggested #thresholdconcepts for #mathmatics, please reply with your suggestion. (I do already have a bunch of research on this, so things like "negative" numbers and sets are strong candidates for threshold concepts.)
Link about threshold concepts (in case this term is unfamiliar): https://www.ee.ucl.ac.uk/~mflanaga/thresholds.html
The idea of proof, the idea of proof by induction and the idea of proof by contradiction are #thresholdconcepts
The idea that mathematics is the study of pattern
The idea that numbers are just equivalence classes
Something about axioms too, as possible whimsical and arbitrary and not necessarily modelling a reality - that mathematics is a game, sometimes with applicability.
The Librarian 🌷
Ed S