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THE                 JOURNAL OF ECONOMIC SCIENCES: THEORY AND PRACTICE, V.82, # 2, 2025, pp. 96-116

                    A.4 Linearization outline and steady state (compact)

                    Linearized IS (consumption Euler):

                                                      
                       =        −   (   −        −    ).                                                                                       (A14)
                                       
                       
                               +1
                                               +1
                                                      
                    Linearized Phillips curve:
                       =          +       .                                                                                                              (A15)
                       
                                           
                                 +1
                    Steady-state relations (symbolic):
                                      
                            
                    1 +   ‾ = 1 +   ‾ −             ,     ‾ =   (  ‾ +   ‾),                                                           (A16)
                    and the static substitution equation:
                                            
                      ‾ −   ‾ =   ‾ +   ‾ (  ‾ −   ‾ ).                                                                                             (A17)
                                                  
                                0
                                      1

                    A.5 Welfare functional and planner FOC
                    Representative-agent welfare:

                                                
                                                 2
                                    
                       = ∑ ∞           [       −    ].                                                                         (A18)
                                             
                                     0
                                                   
                             =0
                                              2
                    Planner’s marginal condition (linear approximation):
                       =      (1 −   ),                                                                                                                    (A19)
                     1
                          2
                                                                              
                    which pins down the interior optimal SDC remuneration            qualitatively (higher   
                    allows a higher        ).
                                          

                    Appendix B - Sensitivity snapshot and Welfare Approximation
                    B.1 Sensitivity snapshot
                    Holding      = −10%:

                       ●     = 0.0:      = 0.8 × 1 × (−0.10) = −8.0%.


                       ●     = 0.8:      = 0.8 × 0.2 × (−0.10) = −1.6%.

                       ●     = 0.6,    = 0.6:      = 0.6 × 0.4 × (−0.10) = −2.4%.


                    B.2   Consumption-equivalent       welfare    approximation     (method)
                    For small welfare perturbations, compute consumption-equivalent    solving:




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