= Normal surface coordinates
{title2=$x\in\mathbb Z_{\geq0}^{7t}$}
For $t$ <tetrahedra>, count the seven <disk> types in each <tetrahedron>. Across each glued face the counts of each of its three normal arc types must agree. These are homogeneous <linear equations> with integer coefficients. An admissible solution also has at most one nonzero quadrilateral type in each <tetrahedron>. Matching the arcs in their <boundary> order reconstructs the <normal surface> up to an <isotopy> preserving the <tetrahedra>.
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