input: Write a function to check if two strings are anagrams of each other.
  assert is_anagram("listen", "silent") == True
  assert is_anagram("hello", "bello") == False
  assert is_anagram("Dormitory", "Dirty room") == True
output: def is_anagram(s1, s2):
      s1 = ''.join(s1.lower().split())
      s2 = ''.join(s2.lower().split())
      return sorted(s1) == sorted(s2)