pd-code-pre-nxt

Build deterministic predecessor and successor maps for every PD-code arc label.

Installation

pip install pd-code-pre-nxt

Usage example

from pd_code_pre_nxt import get_pre_nxt

pd = [[1, 5, 2, 4], [3, 1, 4, 6], [5, 3, 6, 2]]
pre, nxt = get_pre_nxt(pd)
print(nxt[1], pre[1])

Algorithm

Opposite crossing slots define the component graph. Each component must be a two-regular cycle, with a special deterministic treatment for two-label cycles. The smallest label is chosen as the cycle start; both traversal directions are compared lexicographically and the canonical one defines pre and nxt. Numeric suffixes are supported for temporary prefixed labels used during connected sums.

Input conventions

A PD code is represented as a list of four-entry crossings. Arc labels normally occur exactly twice. Public functions validate inputs and return new values rather than mutating caller-owned data unless their API explicitly says otherwise.

External software

No external software is required.

Development

Run examples and package checks before release. Python packages require Python 3.10 or newer. Build PyPI artifacts with:

poetry check
poetry build

License

MIT. See LICENSE.