on Fri Sep 30 2011, Brian Allison
It's not an issue of chafing, but accepting the OPs claim to be true requires the quoted sentence to be nonsensical.
No
I'm not sure of any useful algebra where a member can be both X and non-X simultaneously. If there is one, please share?
"Singular" defines a concept: Saying it is "Singular" doesn't say anything else meaningful about an iterator beyond what's in that concept: self-assignment and destruction. It doesn't even guarantee that the other operations will compile, since the compiler is allowed to detect them as an expression of undefined behavior. All nonsingular iterators conform to a concept that refines "Singular." This is no less a "useful algebra" (whatever that means) than any other concept refinement relationship.
However, refuting the OPs claim has not even an apparent contradiction either to the standard or to my own understanding of fundamental logic.
I don't know what that means either. -- Dave Abrahams BoostPro Computing http://www.boostpro.com