OpenCascade’s kernel forces you to deal with periodicity in topology (the shape structure), while Parasolid handles it in geometry (the math). A cylinder is mathematically continuous because there's no actual "seam" where it starts and ends. But in OpenCascade there’s a seam from 0 to 2π and this seam edge becomes a real topological entity that every algorithm has to deal with.

In Parasolid the cylinder is periodic so when you query a point at U=2.1π, the kernel just knows that's equivalent to U=0.1π. The periodicity is a property of the surface math, not the shape structure. It’s not using polygons/edges/vertexes but a system of equations to calculate the surfaces.

This is why boolean ops fail so often in FreeCAD: it’s asking the kernel to intersect with an artificial edge that shouldn't exist. The seam creates edge cases in intersection calculations, makes filleting near seams a nightmare, and complicates things. Parasolid's implicit handling requires smarter surface evaluation code upfront, but then everything else just works.