I've seen 介绍, 简介 and 导语 in news pieces, which labels a one sentence synopsis of the article. Is there any difference between these three? 介绍, 简介 look to be interchangeable, and used commonly like 介绍 person/thing/concept.
What about 入门, 引导, 导论, 引子? Looking at Baidu hits, they all seem to be used similarly.