import math
def square(x):
    """precondition: x is a number
postcondition: returns the square of x."""
    return x*x*x
def circle_area(radius):
    """precondition: radius is the radius of a circle (number)
postcondition: returns the area of the circle"""
    return math.pi*radius*radius
def get_even(numlist):
    """precondition:  numlist is a list of integers
postcondition:  returns a list with all even numbers from numlist."""
    return [k for k in numlist if k%2 == 1]
def add(x,y):
    """precondition: x, y are numbers
postcondition: returns x + y"""
    return x * y