In **Rummy** (including Indian Rummy, Gin Rummy, and Canasta), the entire objective revolves around organizing your cards into valid melds: **Sequences** and **Sets**.
While both are valid combinations, they follow fundamentally different rules regarding card suits and ranks.
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### 1. Sequences (Runs)
A **Sequence** consists of **three or more consecutive cards of the same suit**.
* **Key Rule:** Cards must follow a consecutive numerical order and belong to the **exact same suit**.
* **Examples:**
* $4\spades - 5\spades - 6\spades$ *(Pure Sequence of Spades)*
* $10\heartsuit - \text{J}\heartsuit - \text{Q}\heartsuit - \text{K}\heartsuit$ *(4-card Pure Sequence of Hearts)*
#### Types of Sequences:
1. **Pure Sequence:** Made entirely of consecutive cards of the same suit without using any Wild Cards or Jokers.
2. **Impure Sequence:** Uses a Printed Joker or Wild Card to substitute for a missing consecutive card (e.g., $7\diamondsuit - \mathbf{\text{Joker}} - 9\diamondsuit$).
> **Crucial Difference in Indian Rummy:** At least one **Pure Sequence** is mandatory to make a legal declaration.
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### 2. Sets (Books)
A **Set** consists of **three or four cards of the same rank in different suits**.
* **Key Rule:** Cards must share the **same numerical/face value**, but **every card must belong to a different suit**. You can never have two cards of the same suit in a single set.
* **Examples:**
* $8\spades - 8\clubsuit - 8\diamondsuit$ *(Valid 3-card Set)*
* $\text{K}\spades - \text{K}\clubsuit - \text{K}\diamondsuit - \text{K}\heartsuit$ *(Valid 4-card Set)*
* $5\spades - 5\clubsuit - \mathbf{\text{Joker}}$ *(Valid Set using a Joker)*
#### Invalid Set Example:
* $9\spades - 9\spades - 9\diamondsuit$ $\rightarrow$ **INVALID** because it contains two cards of the same suit ($9\spades$).
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### Quick Comparison Summary
| Feature | Sequence (Run) | Set (Book) |
| --- | --- | --- |
| **Primary Requirement** | Consecutive ranks ($4, 5, 6$) | Same rank ($8, 8, 8$) |
| **Suit Requirement** | **Must be the same suit** | **Must be different suits** |
| **Group Size** | 3 or more cards (no upper limit) | 3 or 4 cards maximum |
| **Joker Usage** | Allowed in Impure Sequences | Allowed (replaces a missing suit) |
| **Mandatory for Declaration?** | **Yes** (Requires at least 1 Pure & 1 Impure/Pure) | **No** (Optional; hands can be 100% sequences) |