I was just reading the section on short subclauses on the main grammar page, and Bieneke does not seem to give an explanation for why "om" is seemingly omitted at random from certain sentences. This is what is says on the main grammar page "The word om is often omitted. This makes it difficult to see the subclause - the sentence seems to consist of only one main clause, where it actually has a main clause and a subclause, each with its own independent verb. It is important that you recognize the 'omitted-om-construction'. "
Here are some examples
"Ik streef ernaar op tijd te zijn"
"Ik vraag je dat te doen"
"Ik verzoek je op tijd te zijn"
Are there any explanations for this phenomena, or is it just a case of the Dutch picking and choosing when to leave it out and when to put it in.
Any help is much appreciated