Here are some notes about the different HTML 4 entities. The data comes section 24 of the HTML 4 specifications: Character entity references in HTML 4.

Rho

there is no Sigmaf, and no U+03A2 character either

bull

bullet is NOT the same as bullet operator

alefsym

alef symbol is NOT the same as hebrew letter alef, U+05D0 although the same glyph could be used to depict both characters

lArr

ISO 10646 does not say that lArr is the same as the 'is implied by' arrow but also does not have any other character for that function. So ? lArr can be used for 'is implied by' as ISOtech suggests

rArr

ISO 10646 does not say this is the 'implies' character but does not have another character with this function so ? rArr can be used for 'implies' as ISOtech suggests

ni

should there be a more memorable name than 'ni'?

prod

prod is NOT the same character as U+03A0 'greek capital letter pi' though the same glyph might be used for both

sum

sum is NOT the same character as U+03A3 'greek capital letter sigma' though the same glyph might be used for both

sim

tilde operator is NOT the same character as the tilde, U+007E, although the same glyph might be used to represent both

sup

note that nsup, 'not a superset of, U+2283' is not covered by the Symbol font encoding and is not included. Should it be, for symmetry? It is in ISOamsn

sdot

dot operator is NOT the same character as U+00B7 middle dot

lang

lang is NOT the same character as U+003C 'less than' or U+2039 'single left-pointing angle quotation mark'

rang

rang is NOT the same character as U+003E 'greater than' or U+203A 'single right-pointing angle quotation mark'

spades

black here seems to mean filled as opposed to hollow

oelig

ligature is a misnomer, this is a separate character in some languages

lsaquo

lsaquo is proposed but not yet ISO standardized

rsaquo

rsaquo is proposed but not yet ISO standardized

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