remove_bivalent_vertices

remove_bivalent_vertices(k, match_attributes=False)

Remove all degree-2 vertices by splicing their incident edges.

Parameters:

• k (PlanarDiagram) – Diagram to modify (in place).

• match_attributes (bool) – If True, only remove a bivalent vertex when the four adjacent/incident endpoints have matching attributes in pairs (i.e., compatible to splice). If False, remove regardless of attrs.

Returns:

The number of removed bivalent vertices.

Return type:

int

Notes

• Loops are never spliced here.

• For oriented diagrams, vertices whose two outward endpoints have the same direction are skipped (incoherent pairing).