How to "select" a ttk.Checkbutton?

Question

So, with a Tk Checkbutton I just use my_checkbutton.select(), but I cannot fathom out how to do this for a ttk.Checkbutton!

I have 4 Checkbuttons and I want one to be initially pre-selected, the other 3 to be not selected. If I just invoke them with they come up with what looks like a "-" sign, and I can then select & deselect them with the mouse, but th einitial "-" sign needs to be got rid of so they default tohow I want them. Why is it so much more obscure than tk??!!

All sorts, nothing worked as I wanted, returned to Tk instead of ttk, at least I understand how that works.