ZZF2L Piece Deduction

By yoruba and err0rcuber

What is deduction?

During F2L, one of the challenges is determining where your F2L pieces are. Some pieces are visible in plain sight: we can see all of their stickers on the front, top, left and right sides of the cube. However, other F2L pieces are partially or completely hidden from plain sight.

Deduction is the ability to identify them without having to peek at the bottom or back sides. There are 3 levels of deduction:

Easiest: all stickers visible

These are the pieces that have all of the stickers visible on the front, top, left and right sides of the cube. In piece notation, they are the UFR/UFL corners and the UL/UF/UR/FL/FR edges. No deduction is needed.

Medium: corners with 2 stickers visible

These corners (marked in yellow) can be deduced from looking at 2 of their stickers alone, because that's all you need to identify a corner. They are the DFL/DFR/UBL/UBR corners.

To deduce a corner with just 2 stickers:

  • The colours of the 2 stickers mean it could be either one of two corners (that have both colours).
  • The order of the 2 stickers determines which of those two corners it is.

To train this skill, use the Coracle drill (opens in a new tab) by Conrad Rider. Do untimed solves where you try to identify corners with only 2 stickers. After some practice, 'medium' pieces will be as easy to identify as 'easiest' pieces.

Hard: 1 sticker visible

These pieces (marked in red) are impossible to deduce by themselves (UB/BR/BL edges + DBL/DBR corners). You need to look at other pieces to eliminate possibilities.

Process of elimination

A general strategy to deduce 'hard' pieces is to eliminate options based on 'easy' or 'medium' pieces you can see. For example, suppose we want to deduce the BL edge:

Looking at the BL edge alone, we cannot deduce it because we can only see a single (orange) sticker. But we can use the process of elimination on all edges that have orange on them:

  • ❌orange-white (cross edge): cross is already solved, we never consider cross edges.
  • ❌orange-yellow (LL edge): it's at the UF position in plain sight.
  • ❌orange-blue (F2L edge): it's at the UL position in plain sight.
  • ✅orange-green (F2L edge): then orange-green has to be the BL edge.

When you can only see 1 sticker of a piece, there are always 4 options. The nice thing with edges is that you don't need to consider the cross edges because EOCross is already solved, so for edges typically you consider 3 options: one LL edge + two F2L edges.

For corners, you can also use the process of elimination, but it's slightly harder and less consistent. However, if you know exactly what corner you're trying to identify (so a red-green-white for example), you can identify it by just 1 sticker.

This process of elimination becomes easier when more F2L pairs are solved because there are fewer options. With practice, this skill will no longer feel like a detective game. It will become instinct.

LL edge rule

Because EO is solved, there is a rule you can use for the 'hard' UB edge and even the 'easy' FL, FR, UL, and UR edges:


If an edge doesn't have a U sticker on top, it can't be a LL edge. It must be an F2L edge.

U sticker means any sticker that matches the colour of the U center.


Since EOCross is solved, all bottom edges are solved. So during F2L, there are two types of edges: F2L edges (belonging to an F2L pair) and LL edges. LL edges belong to the top (U) layer, so they'll always have a U sticker.

Typically, you need to see both stickers of an edge to tell if it's a LL edge. However, there is a special rule for stickers on the 'purple orbit'. Because EO is solved, U stickers will always be on the purple orbit. This means: if an edge is an LL edge, you will see a U sticker on the purple orbit. If you don't see a U sticker there, the edge is an F2L edge.

You can use this rule together with the process of elimination. Here's an example:

Suppose we want to identify the UB edge. We can only see its top sticker, which is green. Normally, with process of elimination we must consider the three possible edges:

  • ❓green-yellow (LL edge): it's a 'hard' piece, is it at UB or BR?
  • ❌green-red (F2L edge): it's an 'easy' piece, we see it at UF.
  • ❓green-orange (F2L edge): it's a 'hard' piece, is it at UB or BR?

But the LL Edge Rule says: the UB edge doesn't have a U sticker on the purple orbit (it doesn't have yellow there), therefore it's an F2L edge. This is perfect, because it eliminates the green-yellow LL edge which we weren't sure of.

  • ❌green-yellow (LL edge): nope because of UB Edge Rule.
  • ❌green-red (F2L edge): it's an 'easy' piece, we see it at UF.
  • ✅green-orange (F2L edge): green-orange is UB!

Track pieces beforehand

One more strategy for 'hard' pieces is to lookahead during F2L and track pieces that you are not currently solving. Some pieces you track can start visible, but after solving a F2L pair they end up on the back. If you watch where pieces are moving, you can identify a 'hard' piece before it even becomes 'hard'.