Unalterable

The unalterable rhythm of mathematics is definition, theorem, proof.

Source: tatoeba (2028089)

For instance, here is a portrait of a man at eight years old, another at fifteen, another at seventeen, another at twenty-three, and so on. All these are evidently sections, as it were, three-dimensional representations of his four-dimensioned being, which is a fixed and unalterable thing.

Source: tatoeba (3719345)

In the theory of knowledge, as in every other branch of science, we must think dialectically, that is, we must not regard our knowledge as ready-made and unalterable, but must determine how knowledge emerges from ignorance, how incomplete, inexact knowledge becomes more complete and more exact.

Source: tatoeba (13056969)

People of unalterable ideas still insisted upon calling him "Sergeant" when they met him, which was in some degree owing to his having still retained the well-shaped moustache of his military days, and the soldierly bearing inseparable from his form.

Source: wiktionary