import math

#Functions

def pf1(m, n):
    print(m*"*"+n*" "+m*"*")

def pf2(x):
    return (10+x**2)/(1+x**3)

#Conditionals

def pc1(years):
    if years < 0:
        return 'no such era'
    elif years < 70:
        return 'cenozoic'
    elif years < 541:
        return 'paleocoiz'
    elif years < 2800:
        return 'proterozoic'
    elif years < 4000:
        return 'archaic'
    elif years < 4570:
        return 'hadean'
    else:
        return 'no such era'

def pc2(x):
    if x > 0:
        return math.sqrt(x)
    return x**2   #you can also use an else here, but that is one line more

#Lists

def pl1(lst1, lst2):
    result = []
    for element in lst1:
        if element not in lst2:
            result.append(element)
    return result

def pl2(lst1):
    result = []
    for element in lst1:
        result.append(element**2)
    return result

#Strings
def ps1(string):
    counter = 0
    for char in string:
        if char == 'z':
            counter += 1
    return counter

def ps2(string):
    result = []
    for char in string:
        if char == 'a':
            result.append('e')
        elif char == 'e':
            result.append('i')
        elif char == 'i':
            result.append('a')
        else:
            result.append(char)
    return ''.join(result)