Originally Nov 30, 2017. (revised 2021,2023) Russell introduced what is often viewed as his most original contribution to mathematical logic: his theory of types—which in essence tries to distinguish between sets, sets of sets, etc. by considering them to be
Bad ideas in type theory
Types as sets and subtypes as subsets. This may be due to confusing usage in mathematical practice where, for example, we often see references to integers as a subset of reals. But in mathematical usage, people generally understand that while