HP 39gs Master Manual page 334

Special editing commands – Undo, multi-select & swap
Unlike most calculators the CAS editing screen has an undo function. If you have performed some operation
that was incorrect then pressing
have more memory to work with and so allow multiple levels of undo, this will only undo a single operation.
However, this can be very convenient at times.
We have seen how the arrow keys can be used to move the highlight within the expression being edited and
to select various parts of it. If you use the SHIFT key then this modifies the results in various ways.
i.
SHIFT
Pressing
SHIFT
the editing tree currently being worked on. This is best seen by experimentation – effectively, if a
number of terms are currently selected, the selection jumps to the single term at the bottom of that
branch.
ii.
SHIFT
Pressing
SHIFT
contents of the CAS editing screen.
iii.
SHIFT
Pressing
SHIFT
current selection is extended to the right, encompassing one more term for each press.
For example, if the current screen showed:
... then pressing
This allows you evaluate or to apply functions to parts of an
expression without having to do it to the entire thing. For
example, pressing
will undo the operation. Unlike programs on the PC which
SHIFT MEMORY
will move the selection immediately to the bottom left corner of the branch of
will move the selection to the top of the tree, effectively selecting the entire
behaves in the same way as it does in a word processor on a PC. The
will result in:
SHIFT
at this point will result in:
ENTER
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