swap
Returns a container with two of its elements swapped.
Syntax

swap(X, i, j)

X
is a linear container 
i
andj
are nonzero integers

Description
If X
is a container and i
and j
integers, then swap(X, i, j)
returns X
with its elements indexed by i
and j
swapped.
Negative indices count from the end of the container.
Examples
v ≔ SequenceVector(10)
(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
swap(v, 1, −1)
(10, 2, 3, 4, 5, 6, 7, 8, 9, 1)