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

export function holeFind(seen: number[], first: number, count: number): number | undefined {
  if (!Number.isInteger(count) || count <= 0) {
    throw new Error('Count must be a positive integer');
  }
  const expectedSequence = stepsOn(first, count);
  return expectedSequence.find((num, index) => !seen.includes(num)) ?? undefined;
}
```