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In page Vim (text editor):

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Vim's forerunner, Stevie (ST Editor for VI Enthusiasts), was created by Tim Thompson for the Atari ST in 1987[1][2] and further developed by Tony Andrews[1][3] and G.R. (Fred) Walter.[4][5] It was one of the first popularized clones of Vi, and did not use Vi's source code. The source code for Vi used the Ed text editor developed under AT&T, and therefore Vi could only be used by those with an AT&T source license.[citation needed] Basing Vim on the source code for Stevie meant the program could be distributed without requiring the AT&T source license.