Triple

Target class: maximal analytic extension
Context triple: [Kruskal–Szekeres coordinates, instanceOf, maximal analytic extension]

• A. extreme point
  An extreme point of a convex set is a point in the set that cannot be expressed as a nontrivial convex combination of other distinct points from the set.
• B. Eddington–Finkelstein coordinate system
  The Eddington–Finkelstein coordinate system is a reformulation of the Schwarzschild spacetime using null (lightlike) coordinates that smoothly extend across the event horizon, eliminating the coordinate singularity present in standard Schwarzschild coordinates.
• C. Penrose diagram
  A Penrose diagram is a spacetime diagram used in general relativity that compactifies infinite regions to finite size, allowing the global causal structure of a spacetime to be visualized.
• D. Lorentzian manifold
  A Lorentzian manifold is a smooth manifold equipped with a metric tensor of signature \((-+\cdots+)\) (or its variants) that models spacetime in general relativity by distinguishing timelike, spacelike, and null directions.
• E. pseudo-Riemannian manifold
  A pseudo-Riemannian manifold is a smooth manifold equipped with a nondegenerate, symmetric metric tensor of arbitrary signature that allows measurement of lengths and angles, including those with indefinite sign as in spacetime geometry.
• F. None of above. chosen