# Clojure的logic库中cond系列函数的区别

Clojure的逻辑编程库中有一系列的cond函数，都带有“如果”的基本含义，但是又有细微的区别，这里主要对conde、conda、condu这三个函数进行语义上的区分。

# 第一讲: The Learning Problem

## 什么是机器学习？（Key Essence of Machine Learning）

Machine Learning: improving some performance measure with experience computed from data

data $\to$ ML $\to$ improved performance measure

# how to get the data of a specific worksheet of one Google spreadsheet by gid

If we only want to get the data of the first worksheet of the spreadsheet, we don’t need to care about the gid in url, because the gid of this worksheet is always 0 by default. So we can just get the data of the first worksheet by the following request urls:

In the two request urls, the key (also called spreadsheet-id) is unique to each spreadsheet, which can be fetched from the url of the spreadsheet; the option alt=json is the return type of the worksheet data, which can be alt=xml as well, or you can just leave it blank.