used as abbreviation for standard numerals (Typographical Number Theory). For example, using HTML style "4̅" is a shorthand for the standard numeral "SSSS0".
オーバーライン
数式の上に引かれたオーバーラインは、ゲーデル数を表すことがある。例えば A ∨ B は、論理式 A ∨ B のゲーデル数を意味する。
negated ⊢, the sign for "does not prove", for example T ⊬ P says "P is not a theorem of T"
U+22AD⊭not true
is not true of
U+22BC⊼nand
NAND operator. In HTML, it can also be produced by <span style="text-decoration: overline">∧</span>: ∧
U+22BD⊽nor
NOR operator. In HTML, it can also be produced by <span style="text-decoration: overline">∨</span>: ∨
U+25C7◇white diamond
modal operator for "it is possible that", "it is not necessarily not" or rarely "it is not provable not" (in most modal logics it is defined as "¬◻¬")
U+22C6⋆star operator
usually used for ad-hoc operators
U+22A5⊥up tack
U+2193↓downwards arrow
Webb-operator or Peirce arrow, the sign for NOR. Confusingly, "⊥" is also the sign for contradiction or absurdity.
U+2310⌐reversed not sign
U+231C⌜top left corner
U+231D⌝top right corner
corner quotes, also called "Quine quotes"; for quasi-quotation, i.e. quoting specific context of unspecified ("variable") expressions;[2] also used for denoting Gödel number;[3] for example "⌜G⌝" denotes the Gödel number of G. (Typographical note: although the quotes appears as a "pair" in unicode (231C and 231D), they are not symmetrical in some fonts. And in some fonts (for example Arial) they are only symmetrical in certain sizes. Alternatively the quotes can be rendered as ⌈ and ⌉ (U+2308 and U+2309) or by using a negation symbol and a reversed negation symbol ⌐ ¬ in superscript mode. )
Note that the following operators are rarely supported by natively installed fonts. If you wish to use these in a web page, you should always embed the necessary fonts so the page viewer can see the web page without having the necessary fonts installed in their computer.
U+27E1⟡white concave-sided diamond
U+27E2⟢white concave-sided diamond with leftwards tick
modal operator for was never
U+27E3⟣white concave-sided diamond with rightwards tick
modal operator for will never be
U+27E4⟤white square with leftwards tick
modal operator for was always
U+27E5⟥white square with rightwards tick
modal operator for will always be
U+297D⥽right fish tail
sometimes used for "relation", also used for denoting various ad hoc relations (for example, for denoting "witnessing" in the context of Rosser's trick) The fish hook is also used as strict implication by C.I.Lewis ⥽ , the corresponding LaTeX macro is \strictif. See here for an image of glyph. Added to Unicode 3.2.0.
^Brody, Baruch A. (1973), Logic: theoretical and applied, Prentice-Hall, p. 93, ISBN9780135401460, "We turn now to the second of our connective symbols, the centered dot, which is called the conjunction sign."