Many negated forms, particularly of relations, can be encoded by using the base symbol, together with a combining overlay. Occasionally, both a vertical and a slanted negation are used; which one is often a matter of style. Sometimes the negation is indicated for only part of a symbol. In these cases, the negated relations are encoded directly, and variants can be accessed via the variation selector method described in the next section.
Table 2.7 lists the currently encoded negated mathematical relations for which a variant can be realized via composition, by using U+20D2 combining long vertical line overlay together with a base character. In the table, the part of the description in small caps is the character name of the corresponding standard character; the part in lowercase indicates the variation in appearance.
Table 2.7 Negated Relations Using Vertical Line Overlay
neither a subset of nor equal to with vertical stroke
neither a superset of nor equal to with vertical stroke
does not precede or equal with vertical stroke
does not succeed or equal with vertical stroke
* The representative glyphs shown in the code charts [Charts] were revised in Unicode 4.0 [U4.0] to show the forms with slanted overlay - this matches their existing decomposition using U+0338 combining long solidus overlay (see Section 2.3.2, Representative Glyphs for U+2278 and U+2279 for more information).
Note that the use of a base character together with the slanted negation expressed by U+0338 COMBINING LONG SOLIDUS OVERLAY is equivalent to the use of the precomposed negation (see also the discussion in Section 2.6, Accented Characters). For those symbols for which only a partial vertical stroke is used, use of U+20D2 would not give the intended result; U+FE00 VARIATION SELECTOR-1 is used instead, as described in Section 2.18, Variation Selector.
Table 2.8 lists some of the negated forms of mathematical relations that can only be encoded by using either U+0338 combining long solidus overlay or U+20D2combining long vertical line overlay. (For issues with using 0338 in MathML, see Section 3.2.7, Combining Marks. Depending on the overlay used, the negation has a diagonal or vertical stroke. The part of the description that is in small caps reflects the Unicode character name of the non-negated symbol. Because these are not glyph variants of existing characters, the word “negated” is used instead of “NOT” as in the list above, to indicate that the negation is expressed by the combining character sequence, and not inherent in the character.
In some cases, as seen in the two preceding tables, simply using the generic glyph for the vertical overlay will not give the correct appearance. U+2266 ≦ LESS-THAN OVER EQUAL TO and U+2A99 DOUBLE-LINE EQUAL TO OR LESS-THAN are examples of characters that may require a taller stroke. Similarly, the generic position of the solidus overlay as shown for U+2AC6 SUPERSET OF ABOVE EQUALS SIGN above is not ideal.