Question 1029344
<pre>
 1.  A
 2.  B   / A&#8801;B

 3. Av~B          1, Addition
 4. Bv~A          2, Addition
 5. ~AvB          4, Commutation
 6. A&#8835;B           5, Material implication
 7. ~BvA          3, Commutation
 8. B&#8835;A           7, Material implication
 9. (A&#8835;B)&(B&#8835;A)   6,8, Conjunction
10. A&#8801;B           9, Material equivalence

[Note: Some books use -> for &#8835;, <-> for &#8801;,
also •, &#8896;, for & (and)]
Edwin</pre>