Again, in the previous example we could have instead made the substitution {{MATH_86}} and avoided using Example {{CMD_87}}. In general, any time that you make two successive substitutions in a problem, you could have instead just made one substitution. This one substitution is the {{CMD_88}}composition{{CMD_89}} of the two original substitutions. But sometimes it may not be obvious to make one clever substitution, and so two substitutions makes more sense. The next example helps to demonstrate this.