Difference between == and === in Mathematica

Question

I was under the impression that = is an assignment, == is a numeric comparison, and === is a symbolic comparison (as well as in some o

Answer 1

One important difference is that === always returns True or False. == can return unevaluated (which is why it's useful for representing equations.)

In[7]:= y == x^2 + 1

Out[7]= y == 1 + x^2

In[8]:= y === x^2 + 1

Out[8]= False

There are some interesting cases where == returns unevaluated that are worth being aware of while programming. For example:

In[10]:= {} == 1

Out[10]= {} == 1 

which can affect things like If[foo=={}, , ].