A geometry is built up by minimal moves, called "Pachner moves," in which a given tetrahedron can give rise to daughter tetrahedra o each face. In addition, several tetrahedra can collapse to a single tetrahedron.
A geometry is built by moves, called "Pachner moves."  A tetrahedron can give rise to daughter tetrahedra, and the tetrahedra can fall to a single tetrahedron.