File:Blackboard bold in typewritten notes from Gunning (1966).jpg

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Summary[edit]

Media data and Non-free use rationale
Description	Part of a page from Gunning (1966), a set of typewritten lecture notes which were published directly as provided by the author. This portion shows the mixture of hand-written and type-written symbols, along with "blackboard bold" style letters for R and C achieved by double-striking each letter with significant offset between strikes. Using these symbols for real and complex numbers was new at the time but is now pervasive in technical literature. Gunning, Robert C. (1966) Lectures on Riemann Surfaces. Mathematical Notes. Princeton University Press. p. 1. https://archive.org/details/lecturesonrieman0000unse/page/1/mode/1up
Author or copyright owner	Robert C. Gunning
Source (WP:NFCC#4)	https://archive.org/details/lecturesonrieman0000unse/page/1/mode/1up
Date of publication	1966
Use in article (WP:NFCC#7)	Blackboard bold
Purpose of use in article (WP:NFCC#8)	This is an illustrative image showing a typewritten document from the 1960s near the beginning of the use of 'blackboard bold' type in mathematics.
Not replaceable with free media because (WP:NFCC#1)	The software or website from which the screenshot is taken is copyrighted and not released under a free license, so creation of a free image is not possible.
Not replaceable with textual coverage because (WP:NFCC#1)	A plain textual description does not adequately convey how these symbols were used in context in typewritten documents from 60 years ago. Any other available document published in the 1960s is also going to be copyrighted.
Minimal use (WP:NFCC#3)	This is just a small decontextualized snippet of some mathematical lecture notes. It is not commercially interesting in and of itself. The resolution can't be much lower or the symbols will start to become illegible.
Respect for commercial opportunities (WP:NFCC#2)	The use of a low resolution screenshot from software or a website will not impact the commercial viability of the software or site.
Fair useFair use of copyrighted material in the context of Blackboard bold//en.wikipedia.org/wiki/File:Blackboard_bold_in_typewritten_notes_from_Gunning_(1966).jpgtrue

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To illustrate the subject in question
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qualifies as fair use under United States copyright law. Any other uses of this image, on Wikipedia or elsewhere, may be copyright infringement. See Wikipedia:Non-free content and Wikipedia:Copyrights.
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File history

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	Date/Time	Thumbnail	Dimensions	User	Comment
current	02:07, 26 July 2023		880 × 624 (63 KB)	Jacobolus (talk \| contribs)	make this a bit lower resolution. as it gets smaller it gets worse and worse at illustrating the topic, but this size is probably still okay
	02:02, 26 July 2023	No thumbnail	1,257 × 891 (106 KB)	Jacobolus (talk \| contribs)	This file was reduced to a size where it no longer illustrates the topic
	00:02, 26 July 2023	No thumbnail	375 × 266 (75 KB)	DatBot (talk \| contribs)	Reduce size of non-free image (BOT - disable)
	16:50, 25 July 2023	No thumbnail	1,257 × 891 (106 KB)	Jacobolus (talk \| contribs)	use a slightly lower resolution. any lower and it's going to stop clearly demonstrating the letters in question though
	16:24, 25 July 2023	No thumbnail	1,796 × 1,273 (172 KB)	Jacobolus (talk \| contribs)	Uploading an excerpt from a non-free work using File Upload Wizard

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Blackboard bold

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Orientation	Normal
Horizontal resolution	72 dpi
Vertical resolution	72 dpi
Color space	sRGB