ECMO (ECMO)

a relation between a 2D immaterial entity (the boundary) and a material entity, in which the boundary delimits the material entity

the surface of my skin is a 2D boundary of my body

A 2D boundary may have holes and gaps, but it must be a single connected entity, not an aggregate of several disconnected parts.

Although the boundary is two-dimensional, it exists in three-dimensional space and thus has a 3D shape.

2D_boundary_of

boundary of

is 2D boundary of

is boundary of

2D boundary of