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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