APL (Dyalog Unicode), 4 bytes
\⍨⍳9
How it works
⍳9 ⍝ Integers 1..9
⍨ ⍝ Duplicate argument on each side
\ ⍝ Replicate each element *n* times
Examples
Index Generator: ⍳5 = 1 2 3 4 5
Expand: 2 3 \ 1 4 = 1 1 4 4 4
Commute: +⍨4 = 4 + 4 = 8
APL (Dyalog Unicode), 4 bytes
\⍨⍳9
How it works
⍳9 ⍝ Integers 1..9
⍨ ⍝ Duplicate argument on each side
\ ⍝ Replicate each element *n* times
Examples
Index Generator: ⍳5 = 1 2 3 4 5
Expand: 2 3 \ 1 4 = 1 1 4 4 4
Commute: +⍨4 = 4 + 4 = 8
APL (Dyalog Unicode), 4 bytes
\⍨⍳9
How it works
⍳9 ⍝ Integers 1..9
⍨ ⍝ Duplicate argument on each side
\ ⍝ Replicate each element *n* times
Examples
Index Generator: ⍳5 = 1 2 3 4 5
Expand: 2 3 \ 1 4 = 1 1 4 4 4
Commute: +⍨4 = 4 + 4 = 8
APL (Dyalog Unicode), 4 bytes
\⍨⍳9
How it works
⍳9 ⍝ Integers 1..9
⍨ ⍝ Duplicate argument on each side
\ ⍝ Replicate each element *n* times
Examples
Index Generator: ⍳5 = 1 2 3 4 5
Expand: 2 3 \ 1 4 = 1 1 4 4 4
Commute: +⍨4 = 4 + 4 = 8
APL (Dyalog Unicode), 4 bytes
\⍨⍳9
How it works
⍳9 ⍝ Integers 1..9
⍨ ⍝ Duplicate argument on each side
\ ⍝ Replicate each element *n* times
Examples
Index: ⍳5 = 1 2 3 4 5
Expand: 2 3 \ 1 4 = 1 1 4 4 4
Commute: +⍨4 = 4 + 4 = 8
APL (Dyalog Unicode), 4 bytes
\⍨⍳9
How it works
⍳9 ⍝ Integers 1..9
⍨ ⍝ Duplicate argument on each side
\ ⍝ Replicate each element *n* times
Examples
Index Generator: ⍳5 = 1 2 3 4 5
Expand: 2 3 \ 1 4 = 1 1 4 4 4
Commute: +⍨4 = 4 + 4 = 8
APL (Dyalog Unicode), 4 bytes
\⍨⍳9
How it works
⍳9 ⍝ Integers 1..9
⍨ ⍝ Duplicate argument on each side
\ ⍝ Replicate each element *n* times
Examples
Index: ⍳5 = 1 2 3 4 5
Expand: 2 3 \ 1 4 = 1 1 4 4 4
Commute: +⍨4 = 4 + 4 = 8