Swap
From WikiManual
This swaps the top two values on the integer stack. If there are fewer than two values on the stack, then the operator does nothing.
The following code stores a value of 5 in .up:
.up 5 swap store
This swaps the top two values on the integer stack. If there are fewer than two values on the stack, then the operator does nothing.
The following code stores a value of 5 in .up:
.up 5 swap store