  We introduce several-dozen experimentally-found invariants of Poncelet
N-periodics in the confocal ellipse pair (Elliptic Billiard). Recall this
family is fully defined by two integrals of motion (linear and angular
momentum), so any "new" invariants are dependent upon them. Nevertheless,
proving them may require sophisticated methods. We reference some two-dozen
proofs already contributed. We hope this article will motivate contributions
for those still lacking proof.
