Chapter 8 Identity and Function Symbols. Mathematical functions, e.g., +, –, , δ Identity = (“is”) can be treated as either a dyadic predicate or a function: =(x,y), x=y Definition of Terms : Constants (in the book), combination of constants, and function symbols.
xy(Fx & Fy & ≠(x, y))
Adding functions makes quantified predicate logic more powerful
p. A[t // u] or A[u // t] n, m, =E
Here A[t // u] is any result of substituting t for some or all occurrences of u throghout A.
e.g., A[c // d] could be: Fcd, Fdc, Fcc.