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<!ENTITY rArr "⇒" ><!-- rightwards double arrow, U+21D2 ISOtech -->
<!-- Unicode 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 -->
<!ENTITY dArr "⇓" ><!-- downwards double arrow, U+21D3 ISOamsa -->
<!ENTITY hArr "⇔" ><!-- left right double arrow, U+21D4 ISOamsa -->
<!-- Mathematical Operators -->
<!ENTITY forall "∀" ><!-- for all, U+2200 ISOtech -->
<!ENTITY part "∂" ><!-- partial differential, U+2202 ISOtech -->
<!ENTITY exist "∃" ><!-- there exists, U+2203 ISOtech -->
<!ENTITY empty "∅" ><!-- empty set = null set = diameter, U+2205 ISOamso -->
<!ENTITY nabla "∇" ><!-- nabla = backward difference, U+2207 ISOtech -->
<!ENTITY isin "∈" ><!-- element of, U+2208 ISOtech -->
<!ENTITY notin "∉" ><!-- not an element of, U+2209 ISOtech -->
<!ENTITY ni "∋" ><!-- contains as member, U+220B ISOtech -->
<!-- should there be a more memorable name than ’ni’? -->
<!ENTITY prod "∏" ><!-- n-ary product = product sign, U+220F ISOamsb -->
<!-- prod is NOT the same character as U+03A0 ’greek capital letter pi’ though
the same glyph might be used for both -->
<!ENTITY sum "∑" ><!-- n-ary sumation, U+2211 ISOamsb -->
<!-- sum is NOT the same character as U+03A3 ’greek capital letter sigma’
though the same glyph might be used for both -->
<!ENTITY minus "−" ><!-- minus sign, U+2212 ISOtech -->
<!ENTITY lowast "∗" ><!-- asterisk operator, U+2217 ISOtech -->
<!ENTITY radic "√" ><!-- square root = radical sign, U+221A ISOtech -->
<!ENTITY prop "∝" ><!-- proportional to, U+221D ISOtech -->
<!ENTITY infin "∞" ><!-- infinity, U+221E ISOtech -->
<!ENTITY ang "∠" ><!-- angle, U+2220 ISOamso -->
<!ENTITY and "∧" ><!-- logical and = wedge, U+2227 ISOtech -->
<!ENTITY or "∨" ><!-- logical or = vee, U+2228 ISOtech -->
<!ENTITY cap "∩" ><!-- intersection = cap, U+2229 ISOtech -->
<!ENTITY cup "∪" ><!-- union = cup, U+222A ISOtech -->
<!ENTITY int "∫" ><!-- integral, U+222B ISOtech -->
<!ENTITY there4 "∴" ><!-- therefore, U+2234 ISOtech -->
<!ENTITY sim "∼" ><!-- tilde operator = varies with = similar to, U+223C ISOtech -->
<!-- tilde operator is NOT the same character as the tilde, U+007E,
although the same glyph might be used to represent both -->
<!ENTITY cong "≅" ><!-- approximately equal to, U+2245 ISOtech -->
<!ENTITY asymp "≈" ><!-- almost equal to = asymptotic to, U+2248 ISOamsr -->
<!ENTITY ne "≠" ><!-- not equal to, U+2260 ISOtech -->
<!ENTITY equiv "≡" ><!-- identical to, U+2261 ISOtech -->
<!ENTITY le "≤" ><!-- less-than or equal to, U+2264 ISOtech -->
<!ENTITY ge "≥" ><!-- greater-than or equal to, U+2265 ISOtech -->
<!ENTITY sub "⊂" ><!-- subset of, U+2282 ISOtech -->
<!ENTITY sup "⊃" ><!-- superset of, U+2283 ISOtech -->
<!-- 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 -->
<!ENTITY nsub "⊄" ><!-- not a subset of, U+2284 ISOamsn -->
<!ENTITY sube "⊆" ><!-- subset of or equal to, U+2286 ISOtech -->
<!ENTITY supe "⊇" ><!-- superset of or equal to, U+2287 ISOtech -->
<!ENTITY oplus "⊕" ><!-- circled plus = direct sum, U+2295 ISOamsb -->
<!ENTITY otimes "⊗" ><!-- circled times = vector product, U+2297 ISOamsb -->
<!ENTITY perp "⊥" ><!-- up tack = orthogonal to = perpendicular, U+22A5 ISOtech -->
<!ENTITY sdot "⋅" ><!-- dot operator, U+22C5 ISOamsb -->
<!-- dot operator is NOT the same character as U+00B7 middle dot -->
<!-- Miscellaneous Technical -->
<!ENTITY lceil "⌈" ><!-- left ceiling = apl upstile, U+2308 ISOamsc -->
<!ENTITY rceil "⌉" ><!-- right ceiling, U+2309 ISOamsc -->
<!ENTITY lfloor "⌊" ><!-- left floor = apl downstile, U+230A ISOamsc -->
<!ENTITY rfloor "⌋" ><!-- right floor, U+230B ISOamsc -->
<!ENTITY lang "〈" ><!-- left-pointing angle bracket = bra, U+2329 ISOtech -->
<!-- lang is NOT the same character as U+003C ’less than’
or U+2039 ’single left-pointing angle quotation mark’ -->
<!ENTITY rang "〉" ><!-- right-pointing angle bracket = ket, U+232A ISOtech -->
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Modularization of XHTML
F.1.3. XHTML Mathematical, Greek, and Symbolic Characters