That's not quite right. Rigor means not hand-waving about things that a skeptic might doubt, not skipping corner cases, etc. Formal means doing things like a

That's not quite right. Rigor means not hand-waving about things that a skeptic might doubt, not skipping corner cases, etc. Formal means doing things like a computer -- strictly symbolic analysis that doesn't claim to do the impossible task accurately map back to our informal ideas of what things mean. Formality is across a chasm -- it's the most accurate kind of math we can do, but it can't be trusted to say that a formal proof about say complex numbers actually applies to what you are thinking about when you day "complex numbers". As is said, "It is impossible to pass from the informal by purely formal means." Here's a better explanation: https://www.quora.com/What-is-difference-between-rigorous-and-formal-mathematics https://www.quora.com/What-is-difference-between-rigorous-an...