# Four Decision Trees

*English translation by SOTA – AI Community of the Russian original. Organisers who would like this translation removed can email sota.ai.community@gmail.com.*

*Task 4 of the school stage of the All-Russian School Olympiad (VsOSh) 2025/26 in artificial intelligence (region group I), grades 9–11. The official answer and solution are in a separate file.*

Four simple rules are given in the form of “question trees”, which, depending on various features, assign an object the label 0 or 1. An object is described by three features:<br>
$A$ — a binary feature: 0 or 1;<br>
$B$ — shape: circle, square or triangle;<br>
$C$ — a number (may be any real number)

Tree 1:

*[Figure: see the [original statement](https://siriusolymp.ru/2025/ai).]*

- $B$ = circle?
  - no → $A = 0$?
    - no → Label 0
    - yes → Label 1
  - yes → $C \ge 3$?
    - no → Label 1
    - yes → Label 0

Tree 2:

*[Figure: see the [original statement](https://siriusolymp.ru/2025/ai).]*

- $B$ = square?
  - no → $C \ge 4$?
    - no → Label 0
    - yes → Label 1
  - yes → $A = 0$?
    - no → Label 0
    - yes → Label 1

Tree 3:

*[Figure: see the [original statement](https://siriusolymp.ru/2025/ai).]*

- $A = 1$?
  - no → $C = 3$?
    - no → Label 0
    - yes → Label 1
  - yes → $B$ = triangle?
    - no → Label 1
    - yes → Label 0

Tree 4:

*[Figure: see the [original statement](https://siriusolymp.ru/2025/ai).]*

- $C \ge 2$?
  - no → $A = 1$?
    - no → Label 0
    - yes → Label 1
  - yes → $B$ = square?
    - no → Label 0
    - yes → Label 1

*(The trees above are the translator's transcription of the four tree diagrams.)*

Find the unique object (values of $A$, $B$, $C$) that receives label 1 from all four trees.

**Scoring criterion:** 4 points for each correct answer. Total — 12 points

**Maximum score for the task — 12**