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In the following example, the variable `x`

is stepped before `y`

is stepped
(`and`

is not used); thus, the value of `y`

reflects the updated value of `x`

:

(loop for x from 1 to 9 for y = nil then x collect (list x y)) ;;; => ((1 NIL) (2 2) (3 3) (4 4) (5 5) (6 6) (7 7) (8 8) (9 9))

In the following example, `x`

and `y`

are stepped in parallel (`and`

is used):

(loop for x from 1 to 9 and y = nil then x collect (list x y)) ;;; => ((1 NIL) (2 1) (3 2) (4 3) (5 4) (6 5) (7 6) (8 7) (9 8))