### Artificial IntelligenceAIMA Exercises

Suppose you are given the following axioms:
> 1. $0 \leq 4$.
> 2. $5 \leq 9$.
> 3. ${\forall\,x\;\;} \; \; x \leq x$.
> 4. ${\forall\,x\;\;} \; \; x \leq x+0$.
> 5. ${\forall\,x\;\;} \; \; x+0 \leq x$.
> 6. ${\forall\,x,y\;\;} \; \; x+y \leq y+x$.
> 7. ${\forall\,w,x,y,z\;\;} \; \; w \leq y$ $\wedge$ $x \leq z {\:\;{\Rightarrow}\:\;}$ $w+x \leq y+z$.
> 8. ${\forall\,x,y,z\;\;} \; \; x \leq y \wedge y \leq z \: {\:\;{\Rightarrow}\:\;}\: x \leq z$

1. Give a backward-chaining proof of the sentence $5 \leq 4+9$. (Be sure, of course, to use only the axioms given here, not anything else you may know about arithmetic.) Show only the steps that leads to success, not the irrelevant steps.
2. Give a forward-chaining proof of the sentence $5 \leq 4+9$. Again, show only the steps that lead to success.

Suppose you are given the following axioms:
> 1. $0 \leq 4$.
> 2. $5 \leq 9$.
> 3. ${\forall\,x\;\;} \; \; x \leq x$.
> 4. ${\forall\,x\;\;} \; \; x \leq x+0$.
> 5. ${\forall\,x\;\;} \; \; x+0 \leq x$.
> 6. ${\forall\,x,y\;\;} \; \; x+y \leq y+x$.
> 7. ${\forall\,w,x,y,z\;\;} \; \; w \leq y$ $\wedge$ $x \leq z {\:\;{\Rightarrow}\:\;}$ $w+x \leq y+z$.
> 8. ${\forall\,x,y,z\;\;} \; \; x \leq y \wedge y \leq z \: {\:\;{\Rightarrow}\:\;}\: x \leq z$

1. Give a backward-chaining proof of the sentence $5 \leq 4+9$. (Be sure, of course, to use only the axioms given here, not anything else you may know about arithmetic.) Show only the steps that leads to success, not the irrelevant steps.
2. Give a forward-chaining proof of the sentence $5 \leq 4+9$. Again, show only the steps that lead to success.

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