- Read the guideline before start
You are required to implement the count_occurrences function that takes two parameters:
- phrase: A string in which to count occurrences of a letter.
- letter: The letter whose occurrences need to be counted in the given phrase.
The function should return the number of times the letter appears in the phrase, while being case insensitive.
- count_occurrences("letter", "t")should return- 2
- count_occurrences("abc", "a")should return- 1
- count_occurrences("abc", "d")should return- 0
- count_occurrences("ABC", "a")should return- 1
def count_occurrences(phrase: str, letter: str) -> int:
    """
    Count occurrences of a letter in a phrase (case insensitive).
    :param phrase: The phrase to search within.
    :param letter: The letter to count occurrences of.
    :return: The number of occurrences of the letter in the phrase.
    """- 
The function must be case insensitive. This means that both the phrase and the letter should be treated as if they are in the same case (upper or lower). 
- 
It is recommended to avoid using loops to solve this task. Instead, consider utilizing Python's built-in string functions to simplify the solution.