@martinjuckes This comment is long and dry, but perhaps it will help make my reasoning more understandable. On the other hand, it may prove that my mind is a weird place to hang out!
As I see it, there are two ways to parse the NUG sentence into a logic statement. They are `IF dimensional coordinate variable THEN form x(x)` and `IF form x(x) THEN dimensional coordinate variable` As you know, the contrapositive of a simple logic statement is guaranteed to be true, but the converse and inverse are not. I've written them all out in each case below. For the first way to parse the NUG sentence we get: `statement: IF dimensional coordinate variable THEN form x(x)` `contrapositive: IF NOT form x(x) THEN NOT dimensional coordinate variable` `converse: IF form x(x) THEN dimensional coordinate variable` `inverse: IF NOT dimensional coordinate variable THEN NOT form x(x)` Using these statements to examine different variable forms yields: Form | Dimensional Coordinate? | Something else? | Reasoning ---- | ------------------------- | ----- | --------- x(x) | Maybe | Maybe |Converse may not hold x(i) | No | Yes | Contrapositive holds x(x,i) | No | Yes | Contrapositive holds x(i,j) | No | Yes |Contrapositive holds For the second way to parse the NUG sentence we get: `statement: IF form x(x) THEN dimensional coordinate variable` `contrapositive: IF NOT dimensional coordinate variable THEN NOT form x(x)` `converse: IF dimensional coordinate variable THEN form x(x)` `inverse: IF NOT form x(x) THEN NOT dimensional coordinate variable` Using these other statements to examine different variable forms yields: Form | Dimensional Coordinate? | Something Else? | Reason ---- | ------------------------- | ----- | ------ x(x) | Yes | No | Statement holds x(i) | Maybe | Maybe | Inverse may not hold x(x,i) | Maybe | Maybe | Inverse may not hold x(i,j) | Maybe | Maybe | Inverse may not hold If I parse the NUG sentence the first way, I find that it makes strong statements about what isn't a dimensional coordinate variable, but it leaves open the possibility that a variable of the form "x(x)" might not be a dimensional coordinate variable. If I parse it the second way, I get a strong affirmation that the form "x(x)" is a dimensional coordinate variable, but it leaves open the possibility that all the other forms are dimensional coordinate variables as well. This leads me to choose the first way to parse the NUG sentence and say that I don't think the NUG sentence rules out data variables with the form "x(x)". If I understand your reasoning correctly, you choose the second way to parse the NUG sentence. This rules out data variables of the form "x(x)", but I think it doesn't say enough about other forms to be useful. To get to where we would like to be (assuming we don't want to allow data variables with the form "x(x)") I believe we need language in NUG/CF that asserts both `IF dimensional coordinate variable THEN form x(x)` and `IF NOT dimensional coordinate variable THEN NOT form x(x) I don't think we have that language in the current documents. I may have missed it, but I haven't seen it yet. -- You are receiving this because you are subscribed to this thread. Reply to this email directly or view it on GitHub: https://github.com/cf-convention/cf-conventions/issues/174#issuecomment-596816563 This list forwards relevant notifications from Github. It is distinct from [email protected], although if you do nothing, a subscription to the UCAR list will result in a subscription to this list. To unsubscribe from this list only, send a message to [email protected].
