def a(x):
    """prec: x is a list of strings
    postc: reeturns the strings in x  in the first half of the alphabet, 
    case insensitive."""

def super_sum(f, n):
    """prec: f is a function defined on the nonnegative integers
    n is a nonnegative integer.
    postc: return sum(f(k), k = 1..n)
    """

def intersect(A, B):
    """
    prec: A, B are sets
    post: returns a set with all elements in A and B."""