How do U+2571..U+2573 connect?

[Harriet Riddle]

U+2571, U+2572 and U+2573 are 0xA2AC, 0xA2AD and 0xA2AE respectively in 
Big5 (the dominant pre-Unicode encoding for Traditional Chinese). They 
also appear in GBK (Simplified Chinese) as 0xA875, 0xA876 and 0xA877 
respectively, though GBK is post-Unicode (extending GB2312-as-EUC-CN to 
include the entire original URO and some other (non-Hangul) chars from 
other CJK encodings, in this case from Big5).

IBM calls them SH020080, SH030080 and SH040080 respectively (the "8" 
here is just a fullwidth attribute, but they don't seem to appear in 
single-byte code pages as e.g. SH020000 anywhere). They appear, 
unsurprisingly, in the Traditional Chinese code pages, and in the 
versions of the Simplified Chinese code pages expanded for GBK; they 
also appear in the more expanded versions of Japanese EBCDIC for some 
reason.

Also, yes, U+2571 and U+2572 (but not U+2573) appear in the G2 set of 
Videotex Data Syntax 3 / NAPLPS (ITU T.101 Annex D, ANSI X3.110:1983, 
CSA T500:1983, FIPS PUB 121), which has ISO-IR registration numbers 99 
(registered by ANSI and later withdrawn in favour of the redundant 128) 
and 128 (registered by the ITU). Although it is itself a modified 
version of the ISO 6937 set, the base ISO 6937 set doesn't include these 
characters.

--Har

Rebecca Bettencourt via Unicode wrote:
> These three box drawing diagonals appear in at least:
> - Amstrad CPC
> - Mattel Aquarius
> - Atari 8-bit
> - MSX
> - PETSCII
> - Kaypro
> - Sharp MZ
> - Ohio Scientific
> - Robotron
>
> See page 11 of: 
> https://www.unicode.org/L2/L2019/19025-aux-LegacyComputingSources.pdf
>
> See page 5 of: 
> https://www.unicode.org/L2/L2021/21235-terminals-supplement-sources.pdf
>
> They don't appear in Teletext.
>
> As to how they came to be in Unicode originally, I don't know. 
> Probably some IBM or DEC character set.
>
> -- Rebecca Bettencourt
>

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