UnsameQ

lhs =!= rhs evaluates to False if lhs and rhs are identical after evaluation, True otherwise.

Attributes[UnsameQ] := {Protected}

Simple examples

In[1]:= a=!=a
Out[1]= False

In[2]:= 5 =!= 5
Out[2]= False

In[3]:= a=!=b
Out[3]= True