• Alias: [[. • Compound operator with built-in evaluation rules. • mi,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 also: \[RawLeftBracket] , \[LeftDoubleBracketingBar] .
\[LeftDoubleBracket]
[[
i,j, ... 
is by default interpreted as Part[m, i, j, ... ]. 