<p>Intermediate Strategy: Recognizing Blocks</p>
<p>Description: Let’s define a block to be an algebraic expression that appears more than once in a given problem. In SAT problems we can usually treat blocks just like a variable. In particular, blocks should usually not be manipulated - leave them as they are!</p>
<p>Comments: Blocks often appear exactly the same in two places. But sometimes they can appear in two different forms. For example, (a + b + c)/3 can also be written as “the average of a, b, and c.” </p>
<p>When you see a block in a problem there are two ways to handle it:</p>
<p>(1) replace the block by a single variable.
(2) leave the block as is, but think of the block as a single unit that should not be manipulated.</p>