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Vahid Aghajani

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Design a Rate Limiter: The Four-Point Answer, and the Trap
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Design a Rate Limiter: The Four-Point Answer, and the Trap

#systemdesign #programming #softwareengineering #interview
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10 min read
MCP vs API: Why Your Server Needs a /mcp Endpoint (and What You Actually Write)
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MCP vs API: Why Your Server Needs a /mcp Endpoint (and What You Actually Write)

#mcp #programming #ai #python
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9 min read
RTO vs RPO: The Two Numbers That Decide What Disaster Recovery Costs
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RTO vs RPO: The Two Numbers That Decide What Disaster Recovery Costs

#systemdesign #programming #softwareengineering #devops
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15 min read
Cache Invalidation: The Delete Ran, and the Page Is Still Wrong
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Cache Invalidation: The Delete Ran, and the Page Is Still Wrong

#caching #programming #softwareengineering #redis
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17 min read
Continuous Integration vs Continuous Delivery: The Two Halves Almost Nobody Separates
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Continuous Integration vs Continuous Delivery: The Two Halves Almost Nobody Separates

#cicd #programming #softwareengineering
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16 min read
Service Boundaries: Where Does the Line Between Two Services Actually Go?
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Service Boundaries: Where Does the Line Between Two Services Actually Go?

#architecture #programming #softwareengineering #systemdesign
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13 min read
Validating Input at the Edge: Why Four Checks in Four Places Are Worse Than One Border
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Validating Input at the Edge: Why Four Checks in Four Places Are Worse Than One Border

#python #programming #softwareengineering #api
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13 min read
Read Replicas Explained: How to Scale Database Reads Without Shipping a Time-Travel Bug
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Read Replicas Explained: How to Scale Database Reads Without Shipping a Time-Travel Bug

#database #programming #softwareengineering #systemdesign
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10 min read
MVCC and VACUUM: Why Deleting a Million Rows Made Your Table Bigger
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MVCC and VACUUM: Why Deleting a Million Rows Made Your Table Bigger

#postgres #programming #softwareengineering #database
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10 min read
What Is Middleware? The Onion Model, and Why the Order Is the Configuration
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What Is Middleware? The Onion Model, and Why the Order Is the Configuration

#middleware #programming #softwareengineering #webdev
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12 min read
Design Search Autocomplete: The Four-Point Answer, and the Trap
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Design Search Autocomplete: The Four-Point Answer, and the Trap

#systemdesign #programming #softwareengineering #interview
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9 min read
The Ring Buffer: Why a Queue With No Limit Is a Memory Leak (and What Happens When It Fills)
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The Ring Buffer: Why a Queue With No Limit Is a Memory Leak (and What Happens When It Fills)

#computerscience #programming #python #softwareengineering
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15 min read
What Is a Webhook? The Same HTTP Request, With the Arrow Turned Around
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What Is a Webhook? The Same HTTP Request, With the Arrow Turned Around

#webhooks #programming #softwareengineering #api
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9 min read
Read Committed vs Serializable: The Write-Skew Bug Your Default Isolation Level Allows
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Read Committed vs Serializable: The Write-Skew Bug Your Default Isolation Level Allows

#database #programming #softwareengineering #postgres
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8 min read
Design a Web Crawler: The Four-Point Answer, and the \"Polite\" Trap
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Design a Web Crawler: The Four-Point Answer, and the \"Polite\" Trap

#systemdesign #programming #softwareengineering #interview
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7 min read
How Safe Is a 60-Minute Signed URL? The Link Is the Credential
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How Safe Is a 60-Minute Signed URL? The Link Is the Credential

#security #programming #softwareengineering #aws
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9 min read
Design a Notification System: The Four-Point Answer, and the Duplicate-Send Trap
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Design a Notification System: The Four-Point Answer, and the Duplicate-Send Trap

#systemdesign #programming #softwareengineering #interview
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8 min read
Architecture Patterns: The Six Shapes a System Can Take (and Why They Are Not a Menu)
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Architecture Patterns: The Six Shapes a System Can Take (and Why They Are Not a Menu)

#architecture #programming #softwareengineering #systemdesign
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9 min read
SLIs, SLOs and Error Budgets: How to Turn Reliable Enough Into a Number
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SLIs, SLOs and Error Budgets: How to Turn Reliable Enough Into a Number

#sre #programming #softwareengineering #devops
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12 min read
HTTP Caching Explained: max-age, ETag and Why Your Users Still See Last Week's CSS
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HTTP Caching Explained: max-age, ETag and Why Your Users Still See Last Week's CSS

#webdev #programming #softwareengineering #performance
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10 min read
Offset vs Cursor Pagination: Why LIMIT/OFFSET Breaks at Scale (and What to Use Instead)
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Offset vs Cursor Pagination: Why LIMIT/OFFSET Breaks at Scale (and What to Use Instead)

#database #programming #softwareengineering #sql
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8 min read
Running LLMs Locally — Small Models, Quantization, and Your 4GB GPU
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Running LLMs Locally — Small Models, Quantization, and Your 4GB GPU

#llm #ai #machinelearning #programming
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12 min read
Authentication vs Authorization: AuthN vs AuthZ (and Why 401 403)
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Authentication vs Authorization: AuthN vs AuthZ (and Why 401 403)

#llm #api #security #ai
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6 min read
How AI Agents Do Deep Search — Building a Research Agent from Scratch
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How AI Agents Do Deep Search — Building a Research Agent from Scratch

#ai #python #machinelearning #programming
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13 min read
PostGIS vs DuckDB — Choosing the Right Tool for Spatial Data
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PostGIS vs DuckDB — Choosing the Right Tool for Spatial Data

#database #postgres #sql #ai
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11 min read
S3 vs Database Blobs: Why Your Files Don't Belong in Postgres (and What Pre-Signed URLs Fix)
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S3 vs Database Blobs: Why Your Files Don't Belong in Postgres (and What Pre-Signed URLs Fix)

#llm #rag #database #postgres
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6 min read
Pub/Sub vs API Calls: Should Your Services Publish an Event or Just Call Each Other?
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Pub/Sub vs API Calls: Should Your Services Publish an Event or Just Call Each Other?

#api #ai #machinelearning #programming
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5 min read
WMS vs WMTS vs WFS: A Picture, Fast Tiles, or the Raw Data (and When to Use Each)
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WMS vs WMTS vs WFS: A Picture, Fast Tiles, or the Raw Data (and When to Use Each)

#ai #machinelearning #programming
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5 min read
Design a URL Shortener: the Four-Move Answer, and the 301 vs 302 Trap
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Design a URL Shortener: the Four-Move Answer, and the 301 vs 302 Trap

#systemdesign #programming #softwareengineering #interview
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7 min read
Feature Flags vs Load Balancer: One Splits Versions, the Other Splits People
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Feature Flags vs Load Balancer: One Splits Versions, the Other Splits People

#featureflags #programming #softwareengineering #devops
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8 min read
Chaos Engineering vs Load Testing: One Measures the Ceiling, the Other Measures the Floor
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Chaos Engineering vs Load Testing: One Measures the Ceiling, the Other Measures the Floor

#chaosengineering #programming #softwareengineering #devops
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12 min read
Big-O Without the Maths: a Prediction, Not a Measurement
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Big-O Without the Maths: a Prediction, Not a Measurement

#algorithms #programming #python #computerscience
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12 min read
View vs Materialized View: A Saved Question vs a Saved Answer
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View vs Materialized View: A Saved Question vs a Saved Answer

#database #programming #sql #softwareengineering
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8 min read
Hot Keys in a Cache: Why One Key Saturates One Node While the Cluster Looks Idle
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Hot Keys in a Cache: Why One Key Saturates One Node While the Cluster Looks Idle

#caching #programming #systemdesign #softwareengineering
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12 min read
Background Jobs Without a Broker: Your Worker Is Holding a Database Connection for 40 Minutes
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Background Jobs Without a Broker: Your Worker Is Holding a Database Connection for 40 Minutes

#postgres #programming #softwareengineering #backend
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13 min read
Heaps and Priority Queues: The Array That Is Secretly a Tree
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Heaps and Priority Queues: The Array That Is Secretly a Tree

#datastructures #programming #softwareengineering #python
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13 min read
Arrays vs Linked Lists: Why the Textbook Winner Loses on Real Hardware
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Arrays vs Linked Lists: Why the Textbook Winner Loses on Real Hardware

#datastructures #programming #computerscience #performance
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10 min read
Processes vs Threads
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Processes vs Threads

#processesthreads #programming #softwareengineering
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6 min read
Active-Active vs Active-Passive: You Had a Second Server, So Why Were You Down for 41 Minutes?
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Active-Active vs Active-Passive: You Had a Second Server, So Why Were You Down for 41 Minutes?

#systemdesign #programming #softwareengineering #devops
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10 min read
Hash Tables Explained in Detail: Why a Dict Lookup Beats a List Scan by 62,000x
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Hash Tables Explained in Detail: Why a Dict Lookup Beats a List Scan by 62,000x

#python #programming #computerscience #datastructures
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8 min read
Write-Through vs Write-Back Caching — Explained in Detail
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Write-Through vs Write-Back Caching — Explained in Detail

#caching #programming #softwareengineering #systemdesign
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6 min read
Airflow vs Cron: When a Crontab Line Isn't Enough
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Airflow vs Cron: When a Crontab Line Isn't Enough

#airflow #programming #softwareengineering #devops
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6 min read
25 Years of Object Detection in 4 Walls (Sliding Window YOLO DETR)
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25 Years of Object Detection in 4 Walls (Sliding Window YOLO DETR)

#computervision #programming #softwareengineering
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5 min read
Ollama vs vLLM: Local Dev Tool or Production Inference Engine?
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Ollama vs vLLM: Local Dev Tool or Production Inference Engine?

#ollamavsvllm #programming #softwareengineering
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3 min read
Autoscaling Explained: Why New Servers Always Arrive Two Minutes Too Late
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Autoscaling Explained: Why New Servers Always Arrive Two Minutes Too Late

#systemdesign #programming #softwareengineering #devops
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8 min read
Debouncing vs Throttling: Only the Last Event, or the Ones in Between?
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Debouncing vs Throttling: Only the Last Event, or the Ones in Between?

#javascript #programming #webdev #performance
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6 min read
Proximity Search: How \"Restaurants Near Me\" Doesn't Scan Every Restaurant
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Proximity Search: How \"Restaurants Near Me\" Doesn't Scan Every Restaurant

#database #programming #softwareengineering #systemdesign
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6 min read
At-Least-Once vs Exactly-Once Delivery: Why the Customer Got Charged Twice
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At-Least-Once vs Exactly-Once Delivery: Why the Customer Got Charged Twice

#distributedsystems #programming #softwareengineering #systemdesign
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7 min read
Chain of Thought — why 'think step by step' actually works
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Chain of Thought — why 'think step by step' actually works

#chainofthoughtprompting #programming #softwareengineering
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5 min read
Quantization vs Distillation
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Quantization vs Distillation

#quantizationdistillation #programming #softwareengineering
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4 min read
Distributed Tracing — how you find which service ate the 3 seconds
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Distributed Tracing — how you find which service ate the 3 seconds

#systemdesignobservability #programming #softwareengineering
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6 min read
SQLite FTS5: How Full-Text Search Actually Works (Inverted Index + BM25)
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SQLite FTS5: How Full-Text Search Actually Works (Inverted Index + BM25)

#sqlite #programming #softwareengineering #database
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6 min read
Next-Token Prediction: How an AI Actually Writes Text (Not Magic — Just Probability)
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Next-Token Prediction: How an AI Actually Writes Text (Not Magic — Just Probability)

#llm #programming #softwareengineering
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5 min read
Speculative Decoding, Explained: Free LLM Speed With Zero Quality Loss
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Speculative Decoding, Explained: Free LLM Speed With Zero Quality Loss

#speculativedecoding #programming #softwareengineering
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5 min read
Data Modeling Explained: From One Messy Table to a Real Schema
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Data Modeling Explained: From One Messy Table to a Real Schema

#datamodelingindataengineering #programming #softwareengineering
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6 min read
GeoParquet Explained: Your Geodata Has Two Shapes (One You Edit, One You Scan)
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GeoParquet Explained: Your Geodata Has Two Shapes (One You Edit, One You Scan)

#gis #programming #softwareengineering #database
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8 min read
Connection Pooling: Why Your API Dies at 200 Users (But the DB Is at 4% CPU)
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Connection Pooling: Why Your API Dies at 200 Users (But the DB Is at 4% CPU)

#database #programming #softwareengineering #backend
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6 min read
Zero-Shot vs Few-Shot Prompting: Why Your LLM Output Keeps Breaking (and the 1-Minute Fix)
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Zero-Shot vs Few-Shot Prompting: Why Your LLM Output Keeps Breaking (and the 1-Minute Fix)

#promptengineering #programming #softwareengineering
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4 min read
The N+1 Query Problem: Why 100 Products Cost 101 Queries (and Why an Index Won't Save You)
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The N+1 Query Problem: Why 100 Products Cost 101 Queries (and Why an Index Won't Save You)

#database #programming #softwareengineering #performance
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5 min read
How a Database Index Actually Works: B-Trees, Seq Scans, and the Cost Nobody Mentions
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How a Database Index Actually Works: B-Trees, Seq Scans, and the Cost Nobody Mentions

#database #sql #programming #softwareengineering
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6 min read
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