What would be "tiefliegendes Ergebnis" in English?

Question

In German textbooks one sometimes finds the term "tiefliegendes Ergebnis" for theorems whose proofs require strong methods. The literal translation would be "deep lying result" but I'm pretty sure that I have never read this phrase in any English textbook.

So does anyone know a correct translation?

Answer 1

The word 'profound' works for both the figurative and literal meaning of 'tiefliegend':

1a : having intellectual depth and insight
  b : difficult to fathom or understand
2a : extending far below the surface
  b : coming from, reaching to, or situated at a depth

(source: Merriam Webster)

So 'profound result' may be what you're looking for.

Answer 2

I would foster the use of "deep" as in "Deep result", subsequent to the comments by lulu, and by David C.U.

Exemplary usage by Math pros:
https://mathoverflow.net/questions/139607/what-are-some-deep-theorems-and-why-are-they-considered-deep

https://gowers.wordpress.com/2008/07/25/what-is-deep-mathematics/

Withstanding the given Merriam-Webster-ian answer let me note that beside the English "profound" there is the French "profond" being the Latin-based etymological precursor of all, which also made it into German as "profund". And replacing the latter by "tiefliegend" would not be a completely synonymous substitution there.