i have trouble with understand this type of questions ,
i know how i can determine if the sentences is valid or unsatisfiable in Propositional logic , but in FOL i can't
for example , i have the following sentences in FOL :
1 = 2
the professor said this is neither valid nor unsatisfiable
but , i think it is always unsatisfiable , because 1 != 2 !!!
can someone explain to me how can i answer this type of question
thank you all