# VisibleList _ List -- get some entries of a list

## Synopsis

• Operator: _
• Usage:
w_{i,j,...}
• Inputs:
• w,
• {i,j,...}, a list of integers to serve as indices
• Outputs:
• , the list of entries {w_i, w_j, ...}

## Description

The entries of w are numbered starting with 0. If i is negative, then the i-th entry counting from the end is provided. If i is out of range, an error is signaled.

 i1 : w = {a,b,c,d,e,f,g,h} o1 = {a, b, c, d, e, f, g, h} o1 : List i2 : w_{1,3,4} o2 = {b, d, e} o2 : List i3 : w_{-1,-2,-3} o3 = {h, g, f} o3 : List

We can use this operation to compute composition of permutations represented as lists.

 i4 : {4,2,3,1,0} _ {2,1,3,4,0} o4 = {3, 2, 1, 0, 4} o4 : List

Remark: any subscripts that are sequences will have their elements spliced into the rest of the list.

 i5 : {a,b,c,d,e}_{2..4} o5 = {c, d, e} o5 : List