```ts
export function addOne(tally: Record<string, number>, name: string, amount: number): Record<string, number> {
  if (typeof tally[name] === 'undefined') {
    tally[name] = 0;
  }
  tally[name] += amount;
  return tally;
}

export function mergeTally(left: Record<string, number>, right: Record<string, number>): Record<string, number> {
  const combined: Record<string, number> = { ...left };
  for (const name in right) {
    if (right.hasOwnProperty(name)) {
      combined[name] = (combined[name] || 0) + right[name];
    }
  }
  return combined;
}
```