This post continues the investigation into the origin of U+237C ⍼ RIGHT ANGLE WITH DOWNWARDS ZIGZAG ARROW, a character in the Unicode standard. The character was taken from the STIX project, which compiled character tables from many sources including ISO/IEC TR 9573-13. The origin of this technical report for SGML was traced to Anders Berglund, who confirmed that the entity sets came from ISO/IEC 8859, MathSci from the AMS, and Monotype typeface catalogues, including the punch set containing U+237C. However, the specific Monotype catalogue could not be determined due to missing information. A potential source, a List of Mathematical Characters, was found at the Cambridge University Library but requesting a copy would cost 174£.
https://ionathan.ch/2023/06/06/angarr.html