WA3IYC wrote:

No, I mean "knowledge of". Skills are a form of knowledge, as are facts and
concepts. Perhaps it would be better to write "practical knowledge"

For example, consider base 10 natural number arithmetic

"2 + 2 = 4" is a fact.

"Addition is a mathematical operation in which two numbers are combined to get
a third number which is never less than either of the first two numbers" is a
concept.


Not quite. What if the numbers are 2 and -8? Negative numbers are
valid numbers.....
Mathematicians have fun with this sort of thing. Called "proofs", which
I never did
really understand in calculus class anyway.