K-core
= K-core
{title2=$C_k(G)$}
The unique maximal <induced subgraph> with minimum <vertex degree> at least $k$, possibly empty. It is found by repeatedly deleting vertices of degree below $k$. The <k-core peeling invariant> proves that every subgraph satisfying that degree bound survives inside the result; in particular the final vertex set does not depend on deletion order.