I'm reading some papers on the unknotting problem in Knot theory and am running into some notation I don't know (my exposure to topology is minimal, but I have seen it in Analysis courses, Algebra, and just general reading). Suggestions on what to google to get a definition or the definitions themselves would be great. They are the following:
For a link K, what is N(K)?
For a disc D what is $\partial$D?
What is cl(*) (It appeared in the context of a surface S embedded in a 3-manifold M and cutting M along S to create a compact manifold cl(M-N(S)))
These things come up in several papers when I'm reading about Haken's algorithm. For example in here: http://people.maths.ox.ac.uk/lackenby/ekt11214.pdf
To sum up the comments:
$N(K)$ is a tubular neighborhood of your knot, or surface, respectively.
$\text{cl}(A)$ is the closure of a set $A$.
$\partial D^2$ is the boundary circle of the disc $D^2$. Be careful: this is not the same as the notion of boundary of a subset of a space, but rather is a special case of the notion of the boundary of a manifold.