SICP

Functions and the Processes They Generate

We have used primitive arithmetic operations, we have combined these operations, and we have abstracted these composite operations by declaring them as compound functions
最基本的元素复合：基本算术操作符复合，
抽象函数化：组合操作符生成复合函数
The ability to visualize the consequences of the actions under consideration is crucial to becoming an expert programmer
A function is a pattern for the _local evolution _of a computational process.
函数是一种计算过程 局部演化 的模式