### 11.2.10 The difference between := and =<

The := and =< assignment operators have different effects when they are used to modify an element of a list contained in a variable, since =< modifies the element by reference. Otherwise, they will have the same effect.

For example, if
Input:

A := [1,2,3]

then
Input:

A[1] := 5

and
Input:

A[1] =< 5

both change A[1] to 5, so A will be [1,5,3], but they do it in different ways. The command A[1] =< 5 changes the middle value in the list that A originally pointed to, and so any other variable pointing to the list will be changed, but A[1] := 5 will create a duplicate list with the middle element of 5, and so any other variable pointing to the original list won’t be affected.
Input:

A:=[0,1,2,3,4]
B:=A
B[3]=<33
A,B

Output:

[0,1,2,33,4],[0,1,2,33,4]

Input:

A:=[0,1,2,3,4]
B:=A
B[3]:=33
A,B

Output:

[0,1,2,3,4],[0,1,2,33,4]

If B is set equal to a copy of A instead of A, then changing B won’t affect A.
Input:

A:=[0,1,2,3,4]
B:=copy(A)
B[3]=<33
A,B

Output:

[0,1,2,3,4],[0,1,2,33,4]