Spaces between sentences

In the old days of typewriters and nonproportional fonts （in which every letter, from i to w, takes up the same space）, the rule was to put two spaces between sentences to improve readability. But if you print from a computer, you should put just one space between sentences. And speaking of spaces, in the course of revising, cutting and pasting one always ends up with extra spaces strewn throughout a paper. I recommend doing a global find-and-replace when you're done: let the word processor find and replace every extraneous two-space combination with a single space.