Equality ferm,term2 is true under a given interpretation if and only if term,and term2 refer to the same object 。 E.g.,definition of Sibling in terms of Parent: Vx,y Sibling(x,y)(x=y)3m,f(m =f) Parent(m,x)^Parent(f,x)^Parent(m,y)^Parent(f,y)]Equality • term1 = term2 is true under a given interpretation if and only if term1 and term2 refer to the same object • • E.g., definition of Sibling in terms of Parent: • x,y Sibling(x,y)  [(x = y)  m,f  (m = f)  Parent(m,x)  Parent(f,x)  Parent(m,y)  Parent(f,y)]