metamath/valid/induction-sum-odd.mm (28 lines of code) (raw):
${
$d N k x $.
$d k y x $.
$d ph x y $.
induction-sum-odd.0 $e |- ( ph -> N e. NN ) $.
$( (Contributed by Stanislas Polu, 14-Oct-2020.) $)
induction-sum-odd $p |- ( ph -> sum_ k e. ( 1 ... N ) ( ( 2 x. k ) - 1 ) = (
N ^ 2 ) ) $=
( cn wcel c1 cfz co c2 cmul cmin csu cexp caddc oveq2 sumeq1d oveq1 eqeq12d
wceq vx vy cv csn cz 1z ax-mp a1i cc ax-1cn oveq1d 2t1e2 oveq1i 2m1e1 eqtri
fzsn syl6eq sumsn mp2an sq1 syl6eqr wa cuz cfv id syl6eleq cr elfznn adantl
nnuz nnred remulcld 1red resubcld recnd fsump1 ad2antlr nncn sqcld peano2nn 2re
2nn nnmulcld nncnd 1cnd addsubassd binom21 mulcld addassd eqcomd eqtr4d syl
2cnd adddid oveq2i oveq2d 3eqtrd eqtr3d sylan9eqr eqtrd nnindd mpdan )
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$}