  An embedded graph is called $z$-knotted if it contains the unique zigzag (up
to reversing). We consider $z$-knotted triangulations, i.e. $z$-knotted
embedded graphs whose faces are triangles, and describe all cases when the
connected sum of two $z$-knotted triangulations is $z$-knotted.

Combinatorics;Algebraic Topology