This is documentation for Mathematica 3, which was
based on an earlier version of the Wolfram Language.
 Part expr [[ i ]] or Part[ expr , i ] gives the i part of expr. expr [[- i ]] counts from the end. expr [[0]] gives the head of expr. expr [[ i , j , ... ]] or Part[ expr , i , j , ... ] is equivalent to expr [[ i ]] [[ j ]] ... . expr [[ , , ... ]] gives a list of the parts , , ... of expr. You can make an assignment like t [[ i ]] = value to modify part of an expression. When expr is a list, expr [[ , , ... ]] gives a list of parts. In general, the head of expr is applied to the list of parts. You can get a nested listing of parts from expr [[ , , ... ]]. Each part has one index from each list. Notice that lists are used differently in Part than in functions like Extract, MapAt and Position. expr [[ Range[ i , j ] ]] can be used to extract sequences of parts. In StandardForm and InputForm, expr [[ spec ]] can be input as exprspec. and can be entered as [[ and ]] or \[LeftDoubleBracket] and \[RightDoubleBracket]. See the Mathematica book: Section 1.2.4, Section 1.2.4, Section 1.4.6, Section 1.8.4, Section 1.8.4, Section 2.1.4. See also: First, Head, Last, Extract, Position, ReplacePart, MapAt, Take. Related package: LinearAlgebra`MatrixManipulation`. Further Examples This extracts the third element from the list. In[1]:= Out[1]= This extracts a list of elements. In[2]:= Out[2]= The second input resets the third element of the list. In[3]:= Out[3]= In[4]:= Out[4]= In[5]:= Out[5]= In[6]:= This picks out parts 2 and 4 of the sum, leaving their sum. In[7]:= Out[7]=