def contains(x, quarry):
    """prec: x is a list
    postc: returns True if quarry is present in the list."""
    for item in x:
        if item == quarry:
            return True
    return False
def contains_sorted(x, quarry):
    """ prec: x is a sorted list of sortable items (homogeneous)
    postc: return True if quarray is present."""
    if len(x) == 0:
        return False
    if len(x) == 1:
        return x[0] == quarry
    n = len(x) // 2
    if x[n] == quarry:
        return True
    if x[n] < quarry:
        return contains_sorted(x[n:], quarry)
    else:
        return contains_sorted(x[:n], quarry)

x = list(range(2, 200, 7))
print(contains_sorted(x, 49))
print(contains_sorted(x, 51))