51. Is the following Python code valid?
a={3,4,{7,5}}
print(a[2][0])
a={3,4,{7,5}}
print(a[2][0])
a={3,4,{7,5}}
print(a[2][0])
l=[1, 2, 3, 4, 5, 6, 7, 8, 9]
set1 = {1, 2}
set2 = {1, 2, 3, 4}
print(set1.issubset(set2))
{x for x in 'abc'}
{x*3 for x in 'abc'}
>>> a=frozenset(set([5,6,7]))
>>> a
>>> a={5,4}
>>> b={1,2,4,5}
>>> a<b