Classification of simply connected four-dimensional ๐
๐
-manifolds
Classification of simply connected four-dimensional ๐
๐
-manifolds
Let (<italic>M, g</italic>) be a Riemannian manifold. We assume that there is a mapping <inline-formula content-type="math/mathml"> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="s colon upper M right-arrow upper I left-parenthesis upper M right-parenthesis"> <mml:semantics> <mml:mrow> <mml:mi>s</mml:mi> <mml:mo>:</mml:mo> <mml:mi>M</mml:mi> <mml:mo stretchy="false">โ<!-- โ --></mml:mo> <mml:mi>I</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mi>M</mml:mi> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> <mml:annotation encoding="application/x-tex">s:M \to I(M)</mml:annotation> </mml:semantics> โฆ