NaN
A bit of pedantry which has nothing to do with the error in the article: comparing a variable to itself isn't always madness, as it is a specific property of floating point NaN values:
x= NaN
y = x
x != y
A bit of pedantry which has nothing to do with the error in the article: comparing a variable to itself isn't always madness, as it is a specific property of floating point NaN values:
x= NaN
y = x
x != y