First of all, I am an absolute noob regarding music, so please bear with me.
I am trying to understand an exercise (from my son's school lesson, where teacher seems to be reluctant to explain this in detail ...) about solmization with syllables "du da di". I am giving the solution to the exercise question as an image here:
The question reads in english like: Write down the corresponding solmization syllables below the notes.
The question is provided just with the notes, but without the syllables, of course.
I do not understand the rules for when to put what syllable below the notes.
I already did some gooling and searching in here, but could not find a hint about this. Regarding solmization I only find explanation about "do re mi fa so", so it seems to me this "du da di" syllable are some custom stuff.
So my questions are: What kind of rule is behind this solmization? When do I put which syllable in? Is there any general convention about what syllables will be used (du da di) or is this just a convention that each teacher can agree with their students?