LeftDoubleBracket
 Usage
 \[LeftDoubleBracket]
Notes
• Alias:  [[. • Compound operator with built-in evaluation rules. • m i,j, ...  is by default interpreted as Part[m, i, j, ... ]. • Sometimes used in mathematics to indicate a class of algebraic objects with certain variables or extensions. • Extensible character; grows by default to limited size. • See Section 1.10.4 and Section 3.10.4. • See also: \[RawLeftBracket] , \[LeftDoubleBracketingBar] .
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