1. INTRODUCTION  
1.1. Star Formation at \(z\gtrsim7\)  
1.2. Evolution of Stellar Mass Function in Galaxy Clusters  
3. SPITZER DATA REDUCTION AND PROPERTIES  
3.1. Depth and Sky Background  
3.2. Point-Spread Function (PSF)  
4. STAR FORMATION AT \(Z\gtrsim7\)  
5. CONCLUSIONS