Dehn’s lemma

The Dehn’s lemma states that if a continuous map from a2-disk (http://planetmath.org/StandardNBall) to a 3-manifold$f:D^2\to M$ for which $f^{-1}f\partial D^2=D^2$, then there exists an embedding $g:D^2\to M$ such that the restrictions $g|\partial$ and $f|\partial$ areequal.