Here are two more ways of doing the same thing, both using PCX (Curve | Plane intersection) instead of Split with Breps. Version ‘b’ treats all the curves as a flat list, like before:
Delete under XY_2023Mar2b.gh (25.7 KB)
Version ‘c’ keeps the two lists of curves separated by careful attention to data trees. More useful?
Delete under XY_2023Mar2c.gh (32.8 KB)