__ne__ and __eq__

Question

What does it mean?
"If __ne__ is not satisfied, the value opposite to __eq__ is returned."

Answer 1

class eq:
def __init__(self, num):
self.num = num
def __eq__(self, other):
return self.num * other.num == 20
a = b = eq(4)
print(a != b) #True
a = eq(4)
b = eq(5)
print(a != b) #False

Answer 2

This seems to mean, that if you didn't overload the != operator, it executes your __eq__ code and tries to invert it. I don't know which way.

Answer 3

How can I overload != ?