I am writing a document, where I have proved a so-called theorem coming from a physicist paper. It is not a mathematical theorem in the sense that have only done the computations and did not check some necessary hypothesis (differentiability issues).
Is it fair if I say that I give a rigorous proof of the result obtain in the paper [paper name] ?
In this paper I can not find the term "theorem", where do you refer to. I know this theory quite well as it is a foundation of synergetics in physics. In physics unlike math often one presents theories with proof that does not repeat common known contexts/consensus of physicists. In this article I find only one time the word "proof" and that refers to another reference.
The answer to your question is diligently said: yes if you are writing a math paper you can say that and do so.