UndoableNotHistoryIgnorant

# Title: UndoableNotHistoryIgnorant

## Overview

An artificial example illustrating that not every undoable bx is history ignorant. ("History ignorant" has also been termed "strongly undoable" in the past.)

## Models

$M = \{a,b,c\} \times \{false, true\}$

$N = \{a,b,c\}$

## Consistency

Consistency simply ignores the second component of the $M$ model:

$R((x,\_),x)$

## Consistency Restoration

$\overrightarrow{R}((x,\_),y) = x$ (there is no choice here, if the bx is to be correct and hippocratic)

$\overleftarrow{R}((x,\phi),y) = (y, \neg\phi)$ if as sets $\{x,y\} = \{a,c\}$

$\overleftarrow{R}((x,\phi),y) = (y,\phi)$ otherwise.

## Properties

Correct, hippocratic, undoable, not history ignorant.

## Discussion

This is Example 2 from the paper referenced below.

Undoability says that mistakes can be fully undone, provided the initial pair of models was consistent. History ignorance removes the "provided".

The role of $\phi$ here is to mess up the undoing if the models started off inconsistent.

## References [optional section]

@article{DBLP:journals/eceasst/Stevens12,
author = {Perdita Stevens},
title = {Observations relating to the equivalences induced on model sets by bidirectional transformations},
journal = {ECEASST},
volume = {49},
year = {2012},
ee = {http://journal.ub.tu-berlin.de/eceasst/article/view/714},
bibsource = {DBLP, http://dblp.uni-trier.de}
}

Perdita Stevens