public static bool BackwardsMoveNext(ref TraversalEnumerationState state) =>
 -- state.Index >= 0;
 public readonly bool MoveNext <TCollection>(
     TCollection blocks,
     ref TraversalEnumerationState state)
     where TCollection : IReadOnlyList <BasicBlock> =>
 TraversalOrder.BackwardsMoveNext(ref state);
 public static bool ForwardsMoveNext <TCollection>(
     TCollection blocks,
     ref TraversalEnumerationState state)
     where TCollection : IReadOnlyList <BasicBlock> =>
 ++ state.Index < blocks.Count;