Singular TQFTs, foams and type D arc algebras
  We combinatorially describe the $2$-category of singular cobordisms, called (rank one) foams, which governs the functorial version of Khovanov homology. As an application we topologically realize the type $\mathrm{D}$ arc algebra using this singular cobordism construction. 
Michael Ehrig, Daniel Tubbenhauer and Arik Wilbert
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