Learn Dutch: Mocht u de specialist willen bezoeken, dan is de wachtlijst lang. - Should you wish to visit the specialist, then the waiting list is long.

Using the past tense of mogen (mocht) at the start of a sentence is a formal way to create a conditional clause. It translates directly to the English structure "Should you..." (as in, "Should you wish to..."). It makes the situation sound a bit more hypothetical and polite than simply saying Als u de specialist wilt bezoeken.

Could we rewrite this conditional clause into the Nominal Style taught in this lesson?

You generally wouldn't! Nominal style (using a preposition + het + infinitive + van) is great for reducing clauses of time or cause, such as turning Nadat u de specialist bezoekt into Na het bezoeken van de specialist. However, it does not work naturally for purely hypothetical conditional ("if/then") clauses like this one.

Why are there two infinitives (willen bezoeken) at the end of the first clause?

The conjugated verb in this clause is mocht, which is acting as a modal verb. In Dutch, when a modal verb is combined with other verbs, those other verbs are pushed to the end of the clause as infinitives. This creates the double infinitive cluster willen bezoeken.

Is the word dan mandatory before is de wachtlijst lang?