Editing Penrose–Hawking singularity theorems (section)

=== Assumptions of the theorems ===
Typically a singularity theorem has three ingredients:<ref name="penrose_hawking">{{Cite book |first1=Stephen |last1=Hawking |name-list-style=amp |first2=Roger |last2=Penrose |title=The Nature of Space and Time |location=Princeton |publisher=[[Princeton University Press]] |date=1996 |isbn=0-691-03791-4 }}</ref>

# An [[energy conditions|energy condition]] on the matter,
# A condition on the [[global spacetime structure|global structure of spacetime]],
# Gravity is strong enough (somewhere) to trap a region.

There are various possibilities for each ingredient, and each leads to different singularity theorems.