A grammatical problem with verbs

I am writing a paper, and I am stuck into this grammar problem:

As has been proven

As was proven

Which one in correct?

Both are correct, but they have slightly different connotations. "has been" places slight emphasis on the fact that a proof exists, while "was" places slight emphasis on the act of proving it. Given the structure of the phrase, I like the former better.

Understanding the technical time distinction between the two sentences is actually quite useful in practice. The first sentence is set in the present (the present perfect tense) while the second second is set in the past (the simple past tense). Although both sentences may reference the identical past event (that is, the actual proving), each look at this event differently.

The first sentence, set in the present, is concerned with the result of the past's proving, and is unconcerned about when (that is, the time) this event occurred. The second sentence, set in the past, is concerned with the past event itself, and implicitly or explicitly with its time (minute, day, year, century, epoch).

For example,

Last year the mathematician finally proved the theorem. Today, because the theorem has been proved, we can use its results in our experiments.