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64   Life Contingencies

(IA)zR, = I [Cx+2Cx+1+3Cx+2+ ... -}-nCx+n-1] D,

+n) + . . .

Dx   +(Mx+n_1 —Mx+n)]

Also   (la) = 1 [vlx+l +2v21x+2 +3v3lx+3 + ... ] lx

= I [Dx+1 +2Dx+2 +3Dx+3 + ... ] D,

 

1

=

[Nx +Nx+1 +Nx+2 + ... ]

Ds

Sx

Ds

So   (Ia)xn, =

[Dx+1+2Dx+2+3Dx+3+ ... +nDx+n]

Dx

 

) + . . .

+(Nx+n—1 —Nx+n)]

=

Similarly

[Sx—Sx+.n—nNx+n]'

D,

 

 

Sx

(Ia)x = Ds

and (Ia)xnl = - (SxSx+n—nNx+n). D,

12. Suitable commutation symbols may be made for the valuation of assurance and annuity functions involving joint lives. For instance

 

 

axy = — [vlx+1 : Y+1 +v2lx+2 : v+2 + • • • • ]. lxy

So

= — [(Mx Hx+n) + (Hx+i Mx -i-)x [ (N. — Nx+n) + (N.+i —Nx+n

= [Rs —Rx+n —nMx+n]. x


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