In particular in scientific writing, copulae using to be can not only be used to describe the properties of something but also to recapture a definition, to define something or to indicate complete identity. For example, the first of the following sentences gives the definition of a prime number, the second one just describes its properties:
A prime number is a natural number with exactly two divisors.
A prime number is a natural number.
Usually, it is clear from context how a copula is meant to be read, but now I am facing a case where it isn‘t. More specifically, I want a copula or syntactically similar construct to be clearly understood as describing only properties. I am thus looking for verbs or phrases meaning to have the property of being or similar (but less convoluted), i.e.:
A prime number has the property of being a natural number.
I am aware, that as a last resort I can completely rephrase the sentence, e.g.:
Prime numbers are a subset of the natural numbers.
Finally note, that the above are only examples (my actual problem is more complicated and requires background knowledge), so I am not looking for answers specific to this.