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I. INTRODUCTION
II. RELATED WORK AND MOTIVATION
III. FRAMEWORK
IV. EXTENDED REALITY (XR)
V. USER INTERACTIVITY
VI. INTERNET-OF-THINGS (IOT) AND ROBOTICS
VII. ARTIFICIAL INTELLIGENCE
VIII. BLOCKCHAIN
IX. COMPUTER VISION
X. EDGE AND CLOUD
XI. NETWORK
XII. AVATAR
XIII. CONTENT CREATION
XIV. VIRTUAL ECONOMY
XV. SOCIAL ACCEPTABILITY
XVI. PRIVACY AND SECURITY
XVII. TRUST AND ACCOUNTABILITY
XVIII. RESEARCH AGENDA AND GRAND CHALLENGES
XIX. CONCLUDING NOTES
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