Test 1
Write the function is_subset that takes two lists lst1 and lst2 and returns True if all the elements of the lst1 exist in lst2. In other words, the function checks if lst1 is a subset of lst2.
is_subset([1,2,3], [-1,0,1,2,3,4,5]) -> True
is_subset([1,2,3], [2,3,4,5,6,7]) -> False