to_condensed_pd_notation

to_condensed_pd_notation(k)

Serialize a planar diagram to condensed PD notation.

Constraints:

• At most 50 arcs (since we label arcs with single letters).

• Diagram must contain only vertices and crossings.

• No vertex may have degree 4 (ambiguity with crossings).

Parameters:

k (PlanarDiagram) – Diagram to serialize.

Returns:

str – Space-separated tokens of arc letters per node (CCW).

Raises:

ValueError – If constraints are violated.

Return type:

str