let n be Nat; :: thesis: for s being Real_Sequence st ( for n being Nat holds s . n = (n + 1) / (n + 2) ) holds
(Partial_Product s) . n = 1 / (n + 2)
let s be Real_Sequence; :: thesis: ( ( for n being Nat holds s . n = (n + 1) / (n + 2) ) implies (Partial_Product s) . n = 1 / (n + 2) )
defpred S₁[ Nat] means (Partial_Product s) . $1 = 1 / ($1 + 2);
assume A1: for n being Nat holds s . n = (n + 1) / (n + 2) ; :: thesis: (Partial_Product s) . n = 1 / (n + 2)
A2: for n being Nat st S₁[n] holds
S₁[n + 1]

proof

let n be Nat; :: thesis: ( S₁[n] implies S₁[n + 1] )
assume (Partial_Product s) . n = 1 / (n + 2) ; :: thesis: S₁[n + 1]
then (Partial_Product s) . (n + 1) = (1 / (n + 2)) * (s . (n + 1)) by SERIES_3:def 1
.= (1 / (n + 2)) * (((n + 1) + 1) / ((n + 1) + 2)) by A1
.= ((1 / (n + 2)) * (n + 2)) / ((n + 1) + 2) by XCMPLX_1:74
.= 1 / ((n + 1) + 2) by XCMPLX_1:106 ;
hence S₁[n + 1] ; :: thesis: verum

end;

(Partial_Product s) . 0 = s . 0 by SERIES_3:def 1
.= (0 + 1) / (0 + 2) by A1
.= 1 / (0 + 2) ;
then A3: S₁[ 0 ] ;
for n being Nat holds S₁[n] from NAT_1:sch 2(A3, A2);
hence (Partial_Product s) . n = 1 / (n + 2) ; :: thesis: verum