```ts
export function addOne(tally: Record<string, number>, name: string, amount: number): Record<string, number> {
  if (!amount) return tally;
  const existingCount = tally[name] || 0;
  tally[name] = existingCount + amount;
  return tally;
}

export function mergeTally(left: Record<string, number>, right: Record<string, number>): Record<string, number> {
  Object.keys(right).forEach(name => {
    left[name] = (left[name] ?? 0) + right[name];
  });
  return left;
}
```