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

**EDIT:** 

As requested by @Lawrence in the comments, here are some examples of full sentences where "the" is used before "calculus":

1) "The λ-calculus can be called the smallest universal programming language in the world. The λ-calculus consists of a single transformation rule (variable substitution, also called β-conversion) and a single function definition scheme. It was introduced in the 1930s by Alonzo Church as a way of formalizing the concept of effective computability."
Source- https://arxiv.org/pdf/1503.09060.pdf

2) "Church (1936) invented a formal system called the lambda calculus and
defined the notion of computable function via this system." Source- http://www.cse.chalmers.se/research/group/logic/TypesSS05/Extra/geuvers.pdf

3) "The Lambda calculus is an abstract mathematical theory of computation, involving  functions. The lambda calculus can be thought of as the theoretical foundation of functional programming." Source- https://brilliant.org/wiki/lambda-calculus/

In response to @Trevor's comment, we can replace "Euclidean geometry" with "boolean algebra", meaning we're now comparing two types of algebra (linear and boolean).  I haven't heard either of these genres of algebra used with "the" as a prefix, yet they're both 2 sub-branches of the same branch of mathematics.