I've noticed that, when referring to certain branches of calculus,  mathematicians sometimes precede the name of those branches with the word "the".  For example, ["the lambda calculus"][1] or ["the predicate calculus"][2].

To be fair, a Google search turns up plenty of references to "lambda calculus" (without "the" as a prefix).  But it also turns up an equally large number of references to the phrase with the prefix included.  Further, I haven't noticed this with other branches of math.  For example, I haven't heard anyone use the phrase "the linear algebra" or "the Euclidean geometry".  They just say "linear algebra" or "Euclidean geometry".

My question is, why the difference?

  [1]: https://plato.stanford.edu/entries/lambda-calculus/
  [2]: https://www.britannica.com/topic/formal-logic/The-predicate-calculus