Hi igor, just one more note:

> I was able to delete a trim curve on the backside of the
> cylinder,

Yup, that was because it was an interior "hole" boundary, so just that one edge defined an entire trim loop.


> but curve in front got splitted by seam edge of the cylinder and no
> matter what I try it refuses to be deleted))

That's because you were probably not selecting the entire trim boundary, the seam is basically like one of the "outermost" natural edges of the surface, when something intersects it, it becomes part of a longer loop for the exterior trim boundary rather than an interior hole trim.

To remove a boundary you need to select all of its edges (and they must not be attached to any other surface), so in this case with the piece that intersects the seam you must select the seam edges, and the top/bottom edges as well since they are all part of that trim boundary.

- Michael

One method :)
Close the seam by a line
Select this line and one half circle : Net Work
Same for other side

The half arcs circle must be not in one arc line so trim it in 2 arc lines
Network ABCDL in one time dont works!

Another solution :)
Copy rotate the hole circle
Trim keep Cylinder by this new circle
Rotate the new little circle
Union all ;)

Everyone, Thanks!
I was avoing to select all curves as was thinking it will erase my entire shape so i selected only those which formed hole.. - for inner trims it worked but not for the outer boundary trims

I'd better ask no more questions so that Michael had more time for MoI and possibly creating instances feature;))