Morphing
When solving an equation, we often do some operation that involves
rearranging the symbols with minor alterations. Symbol motion covers
this kind of operation. Other times, we need to replace a few symbols
with something else entirely. This happens when we are simplifying
or reducing part of the equation. Some simple examples are if we take
an expression 4x - x and replace it with 3x, or if we take 
and simplify it to x. An alteration like this, applied to the image
of an expression, is called a morph. A morph is when we take
a group of symbols in the image of an equation, and replace it with
a smaller or simpler group of symbols that is mathematically equal.
The concept is not a big deal; that's exactly what you are doing when
you simplify or reduce something, and you do that all the time. So
why do we have a whole chapter about it? The difference is that while
substitution is a mathematical action, morphing is a visual action.
Morphs are often used when doing some kind of substitution, in a broad
sense of the word. There are some patterns we can use that make the
task easier. This chapter explains them and how to use them. We start
with a kind of morph called fusion, and then introduce more
general morphs.