Retrograde Solving is a holistic solve path element in which solvers are presented with the final state of something and need to figure out what it started as. This element is often combined with Transformation Chain puzzles.

## Background

Retrograde Solving has some parallels to detective work in the mystery fiction genre, where a detective has to deduce a sequence of events that led to a final scene. Perhaps the first class of Retrograde Solving puzzles are retrograde analysis chess problems, with noted chess composers such as Sam Loyd creating retrograde analysis problems as early as 1859. The first retrograde analysis book of chess problems, Retrograde Analysis by Dawson and Hundsdorfer, was published in 1915.

## Puzzle Application

Retrograde Solving is essentially the concept of working backwards, and puzzles involving it must be made up of three parts. First, a starting point: in the context of the puzzle, it's most likely going to be the 'ending' point of whatever sequence of events occurred. This could be a single word/phrase, a grid of things, etc. Then, there's the endpoint, AKA the thing needed to solve the puzzle and the thing that, in context, the puzzle 'started' as. Lastly, there's the sequence of events themselves. This is often a series of transformations, a la a Transformation Chain puzzle, but is not necessarily limited to that format. The key is that the sequence has to take the endpoint to the start point, and be able to be used to logically figure out the path back.

As a whole, theming for Retrograde Solving puzzles tends to involve changes of all kinds, allowing solvers to trace them back from one point to another. As a result, Retrograde Solving works very well with meta-theming, particularly the concept of errata. Coupling the puzzle with certain aspects of the puzzle- and hunt-creation process (such as testsolving, solution-writing, and errata) allows for unique theming, giving solvers a look behind the curtain.

## Strategy

### Identification

Retrograde Solving puzzles have a few primary identifiers. As previously mentioned, puzzles with a heavy emphasis on changes, particularly those that have already taken place, have a high likelihood of being Retrograde Solving puzzles. In general, Retrograde Solving puzzles should be relatively easy to identify, between lists of changes/steps/instructions, identifiable 'endpoints', and (commonly) implications that whatever it was originally is important to the puzzle.

### Solving

Like most instructional puzzles, taking these step by step is key. Retrograde Solving puzzles should (in theory) allow solvers to make clear decisions on what needs to be changed and how. Sometimes, this may involve reading ahead and identifying points where a particular state must be achieved, giving you a window of when change has to occur.

TO DO

## Notable Examples

• Piercing the Veil (MITMH 2012) (web) - Presented as a transcript from a program use to write and organize puzzle hunts. Unfortunately for the organizers, that particular puzzle was lost when the writer's computer was run over by a bus. Comments from writers, editors, and testsolvers about the state of the puzzle can be used to recreate the puzzle and solve it the way it was meant to be solved.
• Peaches (GPH 2019) (web) - After playing through the game, solvers are told Click to revealthat there's a way to get a 'secret ingredient' to the phrase GORGEOUS CAKE in only 9 steps (and using each transformation once). Assuming that the secret ingredient is the final answer, solvers then have to work backwards to figure out the only phrase that can accomplish this.
• Guidebook (Puzzle Potluck 4) (web) - In this puzzle, solvers are presented with the solution to a puzzle that doesn't exist on the hunt website. Based on the information in it (which refuses to go into specific detail), solvers need to reconstruct the original puzzle (a 6x6 grid of words).