```ts
export function stepsOn(first: number, count: number): number[] {
  if (count <= 0) throw new Error('Count must be positive');
  return Array.from({ length: count }, (_, i) => first + i);
}

export function holeFind(seen: number[], first: number, count: number): number | undefined {
  const expected = stepsOn(first, count).sort((a, b) => a - b);
  for (let i = 0; i < expected.length; i++) {
    if (!seen.includes(expected[i])) return expected[i];
  }
}
```