How does one trim a polysurface with an INTERSECTING plane or solid?

and why is it so horrendously elusive?

I figured it out, not intuitive, no, but eventually one finds a workaround… why does boolean not work, for example?

Without your geometry it is difficult to impossible to answer your questions.

without an easy way to add an attachment it is difficult to impossible to get anything other than dismissal and denial from your organization

I am not a McNeel employee.

To upload a file click on the vertical arrow icon above where you type your post, or drag the file to where your type your post.

I see that you are a brand new user on this forum. Ordinarily we would welcome you warmly, but not when you seem spring-loaded to assume the worst from the existing users. Perhaps you would like to apologize for your smug sarcastic response, post your file so that people can offer the sort of help that this forum and Rhino users are known for, and spend some time reading various threads to realize I’m not kidding about how helpful people here would like to be if given half a chance.