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Glyph for U+21D4
Source: Noto Sans Math

U+21D4 Left Right Double Arrow

U+21D4 was added in Unicode version 1.1 in 1993. It belongs to the block U+2190 to U+21FF Arrows in the U+0000 to U+FFFF Basic Multilingual Plane.

This character is a Math Symbol and is commonly used, that is, in no specific script.

The glyph is not a composition. Its width in East Asian texts is determined by its context. It can be displayed wide or narrow. In bidirectional text it acts as Other Neutral. When changing direction it is not mirrored. If its East Asian Width is “narrow”, U+21D4 forms a word with similar characters, which prevents a line break inside it. Otherwise it allows line breaks around it, except in some numeric contexts.

The CLDR project calls this character “left right double arrow” for use in screen reading software.

The Wikipedia has the following information about this codepoint:

In logic and related fields such as mathematics and philosophy, "if and only if" (often shortened as "iff") is paraphrased by the biconditional, a logical connective between statements. The biconditional is true in two cases, where either both statements are true or both are false. The connective is biconditional (a statement of material equivalence), and can be likened to the standard material conditional ("only if", equal to "if ... then") combined with its reverse ("if"); hence the name. The result is that the truth of either one of the connected statements requires the truth of the other (i.e. either both statements are true, or both are false), though it is controversial whether the connective thus defined is properly rendered by the English "if and only if"—with its pre-existing meaning. For example, P if and only if Q means that P is true whenever Q is true, and the only case in which P is true is if Q is also true, whereas in the case of P if Q, there could be other scenarios where P is true and Q is false.

In writing, phrases commonly used as alternatives to P "if and only if" Q include: Q is necessary and sufficient for P, for P it is necessary and sufficient that Q, P is equivalent (or materially equivalent) to Q (compare with material implication), P precisely if Q, P precisely (or exactly) when Q, P exactly in case Q, and P just in case Q. Some authors regard "iff" as unsuitable in formal writing; others consider it a "borderline case" and tolerate its use. In logical formulae, logical symbols, such as and , are used instead of these phrases; see § Notation below.

Representations

System Representation
8660
UTF-8 E2 87 94
UTF-16 21 D4
UTF-32 00 00 21 D4
URL-Quoted %E2%87%94
HTML hex reference ⇔
Wrong windows-1252 Mojibake ⇔
HTML named entity ⇔
HTML named entity ⇔
HTML named entity ⇔
HTML named entity ⇔
Encoding: EUC-KR (hex bytes) A2 A2
Encoding: JIS0208 (hex bytes) A2 CE
LATEX \Leftrightarrow
Adobe Glyph List arrowdblboth
Adobe Glyph List dblarrowleft
digraph ==

Related Characters

Elsewhere

Complete Record

Property Value
Age (age) 1.1 (1993)
Unicode Name (na) LEFT RIGHT DOUBLE ARROW
Unicode 1 Name (na1)
Block (blk) Arrows
General Category (gc) Math Symbol
Script (sc) Common
Bidirectional Category (bc) Other Neutral
Combining Class (ccc) Not Reordered
Decomposition Type (dt) none
Decomposition Mapping (dm) Glyph for U+21D4 Left Right Double Arrow
Lowercase (Lower)
Simple Lowercase Mapping (slc) Glyph for U+21D4 Left Right Double Arrow
Lowercase Mapping (lc) Glyph for U+21D4 Left Right Double Arrow
Uppercase (Upper)
Simple Uppercase Mapping (suc) Glyph for U+21D4 Left Right Double Arrow
Uppercase Mapping (uc) Glyph for U+21D4 Left Right Double Arrow
Simple Titlecase Mapping (stc) Glyph for U+21D4 Left Right Double Arrow
Titlecase Mapping (tc) Glyph for U+21D4 Left Right Double Arrow
Case Folding (cf) Glyph for U+21D4 Left Right Double Arrow
ASCII Hex Digit (AHex)
Alphabetic (Alpha)
Bidi Control (Bidi_C)
Bidi Mirrored (Bidi_M)
Composition Exclusion (CE)
Case Ignorable (CI)
Changes When Casefolded (CWCF)
Changes When Casemapped (CWCM)
Changes When NFKC Casefolded (CWKCF)
Changes When Lowercased (CWL)
Changes When Titlecased (CWT)
Changes When Uppercased (CWU)
Cased (Cased)
Full Composition Exclusion (Comp_Ex)
Default Ignorable Code Point (DI)
Dash (Dash)
Deprecated (Dep)
Diacritic (Dia)
Emoji Modifier Base (EBase)
Emoji Component (EComp)
Emoji Modifier (EMod)
Emoji Presentation (EPres)
Emoji (Emoji)
Extender (Ext)
Extended Pictographic (ExtPict)
FC NFKC Closure (FC_NFKC) Glyph for U+21D4 Left Right Double Arrow
Grapheme Cluster Break (GCB) Any
Grapheme Base (Gr_Base)
Grapheme Extend (Gr_Ext)
Grapheme Link (Gr_Link)
Hex Digit (Hex)
Hyphen (Hyphen)
ID Continue (IDC)
ID Start (IDS)
IDS Binary Operator (IDSB)
IDS Trinary Operator and (IDST)
IDSU (IDSU) 0
ID_Compat_Math_Continue (ID_Compat_Math_Continue) 0
ID_Compat_Math_Start (ID_Compat_Math_Start) 0
Ideographic (Ideo)
InCB (InCB) None
Indic Mantra Category (InMC)
Indic Positional Category (InPC) NA
Indic Syllabic Category (InSC) Other
Jamo Short Name (JSN)
Join Control (Join_C)
Logical Order Exception (LOE)
Math (Math)
Noncharacter Code Point (NChar)
NFC Quick Check (NFC_QC) Yes
NFD Quick Check (NFD_QC) Yes
NFKC Casefold (NFKC_CF) Glyph for U+21D4 Left Right Double Arrow
NFKC Quick Check (NFKC_QC) Yes
NFKC_SCF (NFKC_SCF) Glyph for U+21D4 Left Right Double Arrow
NFKD Quick Check (NFKD_QC) Yes
Other Alphabetic (OAlpha)
Other Default Ignorable Code Point (ODI)
Other Grapheme Extend (OGr_Ext)
Other ID Continue (OIDC)
Other ID Start (OIDS)
Other Lowercase (OLower)
Other Math (OMath)
Other Uppercase (OUpper)
Prepended Concatenation Mark (PCM)
Pattern Syntax (Pat_Syn)
Pattern White Space (Pat_WS)
Quotation Mark (QMark)
Regional Indicator (RI)
Radical (Radical)
Sentence Break (SB) Other
Soft Dotted (SD)
Sentence Terminal (STerm)
Terminal Punctuation (Term)
Unified Ideograph (UIdeo)
Variation Selector (VS)
Word Break (WB) Other
White Space (WSpace)
XID Continue (XIDC)
XID Start (XIDS)
Expands On NFC (XO_NFC)
Expands On NFD (XO_NFD)
Expands On NFKC (XO_NFKC)
Expands On NFKD (XO_NFKD)
Bidi Paired Bracket (bpb) Glyph for U+21D4 Left Right Double Arrow
Bidi Paired Bracket Type (bpt) None
East Asian Width (ea) ambiguous
Hangul Syllable Type (hst) Not Applicable
ISO 10646 Comment (isc)
Joining Group (jg) No_Joining_Group
Joining Type (jt) Non Joining
Line Break (lb) Ambiguous (Alphabetic or Ideographic)
Numeric Type (nt) none
Numeric Value (nv) not a number
Simple Case Folding (scf) Glyph for U+21D4 Left Right Double Arrow
Script Extension (scx)
Vertical Orientation (vo) R