generative modeling for Rhino
It's called "Inside" (BRep Inclusion), in "Surface" --> "Analysis" --> 3rd Panel.
When you are stuck with a component you can't find, a good way to find it is to double-click on the canvas and type the name of the component (so in your exemple, "In"). It will give you a selection of components that are named like that or include this keyword.
Got it! thank you so much!!
There is a FAQ that addresses this in more detail.