## Tuesday, October 4, 2011

### EQ 7: Leibniz Axiom and Theorems

(1) Axiom, Leibniz: (e = f) $$\Rightarrow$$ $$E_e^z = E_f^z$$

Note 1: difference between Leibniz Inference Rule and the Leibniz Axiom.

The inference rule states that if X = Y in all states then $$E_X^z = E_Y^z$$ in all states.

The axiom states that if (x = y) in one state then $$E_x^z = E_y^z$$ in that state.

Note 2: the implication is one way. iow $$E_e^z = E_f^z$$ $$\nRightarrow$$ (e = f)

e.g: Let E $$\equiv$$ false $$\wedge$$ zee . Here $$E_e^z = E_f^z$$ but e $$\neq$$ f

Substitution Theorems:

If an equality conjuncts or implies, or a conjunction with an equality as a conjunct implies , an Expression E containing one side of the equality, you can replace that part of E with the other side of the equality.

(2) Theorem: Substitution 1: (e = f) $$\wedge$$ $$E_e^z \equiv$$ (e = f) $$\wedge$$ $$E_f^z$$

(3) Theorem: Substitution 2: (e = f) $$\Rightarrow$$ $$E_e^z \equiv$$ (e = f) $$\Rightarrow$$ $$E_f^z$$

(4) Theorem: Substitution 3: q $$\wedge$$ (e = f) $$\Rightarrow$$ $$E_e^z \equiv$$ q $$\wedge$$ (e = f) $$\Rightarrow$$ $$E_f^z$$

Replace By True Theorems:

If a variable conjuncts or implies, or a conjunction with a variable as a conjunct implies an expression E containing that variable, the occurences of the variable in the expression can be replaced by true

(5) Theorem Replace by true 1: p $$\wedge$$ $$E_p^z \equiv$$ p $$\wedge$$ $$E_{true}^z$$

(6) Theorem: Replace by true 2: p $$\Rightarrow$$ $$E_p^z \equiv$$ p $$\Rightarrow$$ $$E_{true}^z$$

(7) Theorem: Replace by true 3: q $$\wedge$$ p $$\Rightarrow$$ $$E_p^z \equiv$$ q $$\wedge$$ p $$\Rightarrow$$ $$E_{true}^z$$

Example:

Prove p $$\wedge$$ q $$\Rightarrow$$ ( p $$\equiv$$ q)

$$\hspace{2 cm }$$ p $$\wedge$$ q $$\Rightarrow$$ ( p $$\equiv$$ q)

=$$\hspace{0.5 cm }$$ recognize pattern. conjunction with a variable (p) on one side implying an expression containing the same variable
$$\hspace{0.5 cm }$$ invoke Theorem (6) above, replace p in expression by true

$$\hspace{2 cm }$$ p $$\wedge$$ q $$\Rightarrow$$ ( true $$\equiv$$ q)

=$$\hspace{0.5 cm }$$ recognize pattern. conjunction with a variable (q) on one side implying an expression containing the same variable
$$\hspace{0.5 cm }$$ invoke Theorem (6) above, replace q in expression by true

$$\hspace{2 cm }$$ p $$\wedge$$ q $$\Rightarrow$$ ( true $$\equiv$$ true)

=$$\hspace{0.5 cm }$$ Theorem: true is the identity of $$\equiv$$, m $$\equiv$$ m $$\equiv$$ true

$$\hspace{2 cm }$$ p $$\wedge$$ q $$\Rightarrow$$ true

=$$\hspace{0.5 cm }$$ Theorem: true is the Right Zero of $$\Rightarrow$$, m $$\Rightarrow$$ true $$\equiv$$ true

$$\hspace{2 cm }$$ true

Replace By False Theorems:

If an Expression E containing a variable p disjuncts p, implies p or implies a disjunction with p on one side,p can be replaced by false in the expression

(8) Theorem: Replace by False 1: $$E_p^z$$ $$\vee$$ p $$\equiv$$ $$E_{false}^z$$ $$\vee$$ p

(9) Theorem: Replace by False 2: $$E_p^z$$ $$\Rightarrow$$ p $$\equiv$$ $$E_{false}^z$$ $$\Rightarrow$$ p

(10) Theorem: Replace by False 2: $$E_p^z$$ $$\Rightarrow$$ p $$\vee$$ q $$\equiv$$ $$E_{false}^z$$ $$\Rightarrow$$ p $$\vee$$ q

(11) Theorem: Shannon: $$E_p^z$$ $$\equiv$$ ( p $$\wedge$$ $$E_{true}^z$$ ) $$\vee$$ ( $$\neg$$ p $$\wedge$$ $$E_{false}^z$$ )