It is a species of question-begging that assumes as. [definitional]
This fallacy is really a first-class rascal because it sneaks up on us so often. It is a species of question-begging that assumes as true what is to be proved. It is to assume the truth of what one seeks to prove in the effort to prove it.
Ruggero J. Aldisert, Agatha D. Aldisert, Logic for Lawyers- A Guide …, loc. 1162