Alexander Koryagin:

AK> "So  as"  and  "so that" are interchangeable. "So as" is
AK> less common, however.

Maybe you are confusing "so as" with "so as  to"?   If  not,
then  could you cite some examples and dictionary defintions
that show "so as" to be interchangeable with "so that"  when
introducing an adverbial clause of result or purpose?

AS>> Your  quotation  is  in  perfect English, even with the
AS>> classic first-person "should".  Nothing,  however,  was
AS>> replaced  in  the answer, but the verb phrase "take the
AS>> most important examination of your career"  was  simply
AS>> omitted.

AK> As was "speaks" in my previous sentence with "to".

No.  Here is your sentence:

  When  a  person is in a company of friends he never speaks
  formally. And he should not to.

If I reinstate the "speaks" that you say was simply omitted,
the sentence turns into nonsense:

  And he should not to speaks.

You  did not omit "speaks", but rather replaced "speak" with
"to", which is illogical because it vioaltes type safety.

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 * Origin: nntps://fidonews.mine.nu - Lake Ylo - Finland (2:221/6.0)