Add README

README.md

@@ -1,37 +1,80 @@
 ---
-dataset_info:
-  features:
-  - name: prompt
-    dtype: string
-  - name: completion
-    dtype: string
-  - name: answer
-    dtype: string
-  - name: expression
-    dtype: string
-  - name: steps
-    dtype: int64
-  - name: text
-    dtype: string
-  splits:
-  - name: train
-    num_bytes: 12149052
-    num_examples: 15000
-  - name: validation
-    num_bytes: 607770
-    num_examples: 750
-  - name: test
-    num_bytes: 2428870
-    num_examples: 3000
-  download_size: 7567774
-  dataset_size: 15185692
+license: gpl-3.0
+pretty_name: Calculator
+size_categories:
+  - 10K<n<100K
+task_categories:
+  - text-generation
+language:
+  - en
 configs:
-- config_name: default
-  data_files:
-  - split: train
-    path: data/train-*
-  - split: validation
-    path: data/validation-*
-  - split: test
-    path: data/test-*
+  - config_name: default
+    data_files:
+      - split: train
+        path: data/train-*
+      - split: validation
+        path: data/validation-*
+      - split: test
+        path: data/test-*
 ---
+
+# Arithmetic Expression Dataset Generator
+
+## Overview
+
+This is a synthetic deterministic dataset with nested arithmetic expressions and step-by-step solutions. We provide balanced examples of bracketed arithmetic expressions using:
+
+- parentheses: `()`
+- square brackets: `[]`
+- curly braces: `{}`
+
+and operators:
+
+- `+`
+- `-`
+- `*`
+
+The dataset is balanced across reduction depths from 1 to 15 and is intended for SLMs that learn structured mathematical reasoning from examples.
+
+## Content
+
+Each sample contains:
+
+- `expression` — the original arithmetic expression
+- `prompt` — the input prompt for the model
+- `completion` — the target answer in `<think> ... </think>` and `<answer> ... </answer>` format
+- `answer` — the final numeric result
+- `steps` — the number of reduction steps
+- `text` — the full formatted training sample
+
+## Counts
+
+- Train examples: 15000
+- Validation examples: 750
+- Test examples: 3000
+- Total examples: 18750
+
+Each step from 1 to 15 appears exactly:
+- 1000 times in train
+- 50 times in validation
+- 200 times in test
+
+## Example
+
+```text
+### Expression
+Calculate: (11 + (296 - 98))
+
+### Answer
+<think>
+Start: (11 + (296 - 98))
+1. (74 * 4) = 296
+2. (296 - 98) = 198
+3. (11 + 198) = 209
+</think>
+<answer>209</answer>
+```
+
+## Dataset generation
+
+Expressions are generated automatically with random trees and bracket types. The evaluator uses stack-based parsing and operator precedence to produce valid traces. The generator deduplicates expressions so the dataset contains unique samples.