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The Evolution of Retirement by J. Ignacio Conde-Ruiz* Vincenzo ...

The Evolution of Retirement by J. Ignacio Conde-Ruiz* Vincenzo ...

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∂τ t+1<br />

∂w = − δ<br />

(1 + n t+1 ) ϕ +1 + Θ<br />

s µ<br />

1 − δ(wa t+1) 2<br />

2<br />

w t+1<br />

2<br />

− 2[A−(1+r)wa t (1−τ t−δw a t )2 ]<br />

(1+n t )w t+1<br />

where<br />

Θ =<br />

Ã<br />

δ<br />

1 − δ ¡ wt+1<br />

a<br />

(1 + n t+1 ) ϕ +1<br />

¢ 2<br />

!<br />

w t+1<br />

− [(1 + n t+1) ϕ +1] £ A − (1 + r)w a t z t<br />

2 ¤<br />

(1 + n t )(w t+1 ) 2<br />

− (1 + r)z t(z t − 2δw a t )<br />

(1 + n t )w t+1<br />

Notice that we cannot sign ∂τ t+1 /∂w; however, it is easy to show that a sufficient<br />

µ<br />

condition for Θ > 0isthatA w t+1 .<br />

By eq. 12, we thus have that<br />

∂z t+1<br />

∂w<br />

δ<br />

=<br />

(1 + n t+1 ) ϕ +1 − Θ<br />

2(1+n t+1 )(w t+1 ) 2 − δ =<br />

(1 + n t+1 ) ϕ<br />

= −δ<br />

(1 + n t+1 ) ϕ +1 − Θ<br />

2(1+n t+1 )(w t+1 ) 2 < 0<br />

since Θ > 0. Q.E.D.<br />

29

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