print(1, 'empty set', set())
s = set('aeiou')
print(type(s))
print(s)

s = set()
s.add('a')
s.add('b')
print(2, s)

print(3, 'add a')
s.add('a')
print(s)

print(4, '==')  # order does not matter
print( {'c','a','', 'b'} == {'a', 'b', 'c',''} )

print(5,'strings')
basket = {'apple', 'orange', 'apple', 'pear', 'orange', 'banana'}
print('|basket| =',len(basket), 'basket =',basket)
print('stepwise remove')
print(basket)
while basket: # basket not empty
  r = basket.pop() 
  print('removed:', r, 'basket: ', basket) 

print(6,'in')
print('orange' in basket)
print('kiwi' in basket)

print(7,'var a')
a = set('abc')
print(a)


print(8,'var b')
b = set('bcd')
print(b)

print(9,'(a,b)')
print((a,b))

print(10,'a|b')
print(a | b)


print(11,'a&b')
print(a & b)

print(12,'a-b')
print(a - b)

print(13,'a^b')
print(a ^ b)

print(14,'var u: all lower case')
u = set('abcdefghijklmnopqrstuvwxyz')
print('a & u:', a & u)
print('u - a:', u - a)

print(15)
c = {'a','b','c'}
print('a:',a)
print('b:',b)
print('c:',c)
d = {'a','b'}
print('d:',d)

print('a<b:',a<b, '  b<a:',b<a)
print('a<=b:',a<=b, '  b<=a:', b<=a)
print('a<c:',a<c, '  a<=c:',a<=c, 'a>c:', a>c, '  a>=c:', a>=c)
print('a-b:',a-b, '  b-a:',b-a)
print('a-d:',a-d, '  d-a:',d-a)

print('a subset c:',a.issubset(c))
print('a superset c:', a.issuperset(c))
print('c superset d:', c.issuperset(d))
print('a symdiff b:', a.symmetric_difference(b), '==', (a|b)-(a&b),
                      '==', (a-b)|(b-a))

def isPrime(n):
    w = 2
    while w*w<=n:
        if n%w==0:
            return False
        w=w+1
    return True

u=set()
for i in range(32):
   u.add(i)
print('u =', u)

o=set()
for i in range(1,32,2):
    o.add(i)
print('o =', o)

d = set('0123456789')
print('d =', d)

e = u-o
print('e =', e)

p=set()
for i in range(2,32):
    if isPrime(i):
        p.add(i)
print('p =', p)