re: 1 or 2 spaces after a period?

quote:

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1–37. Constructing military correspondence
a. General techniques. When constructing basic military correspondence, focus first on the main point. Use of active
voice is the basic style of Army writing.
b. Specific techniques. Incorporate these plain language techniques to improve effectiveness:
(1) Use short words.
(2) Keep sentences short. The average length of a sentence should be about 15 words.
(3) Write paragraphs that, with few exceptions, are no more than 10 lines.
(4) Avoid jargon.
(5) Use correct spelling, grammar, and punctuation.
(6) Use “I,” “you,” and “we” as subjects of sentences instead of this office, this headquarters, this command, all
individuals, and so forth.
(7) Write one-page letters and memorandums for most correspondence. Use enclosures for additional information.
(8) Avoid sentences that begin with “It is,” “There is,” or “There are.”
(9) Insert two blank spaces after ending punctuation (for example, a period and question mark).
(10) Insert two blank spaces after a colon.
(11) When numbering subparagraphs, insert two blank spaces after the parentheses.

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