In Lesson 1.7, to point out Tanaka is the teacher, we're given the phrase,
たなか せんせい が せんせい です
Tanaka sensei ga sensei desu.
From the content of the lesson, I was expecting to see something like
Tanaka-san ga sensei desu.
But instead, the word for teacher is used twice. Is sensei an alternative honorific in place of -san? And if so, isn't it weird to use it twice in the same sentence like this? If I'm understanding the lesson correctly, this basically says “Teacher Tanaka (is the one that) is the teacher.”