Reason: Proof of P8.4d-1b (lem:van-trees-assembly-scale-set-2026a): constraints, Chernoff exponents, limits and eventual smallness of the majorants.
Proof
Tools. We write T for Real Powers Through the Exponential, and Elementary Asymptotic Tools: Monotonicity, Null Sequences of Negative Powers, Exponential Domination, Integer Rounding, and Square-Root and Exponential Inequalities and use its claims as follows. By T.1 and T.2, for N∈N (so N≥1) and real a,b: Na>0, NaNb=Na+b, (Na)b=Nab, Na≤Nb whenever a≤b, and Na≥1 for a≥0; also (Na)1/2=Na/2 and N1/2=N. By T.3(a) and the scalar-multiple law of Arithmetic of Limits of Real Sequences, cN−a→0 for all real c and a>0; hence, by T.3(d), for every x>0 there is N0 with cN−a<x for all N≥N0 (eventual smallness of powers). By T.3(c), a sequence (uN) with ∣uN−u∣≤vN for all N≥N0 and vN→0 converges to u (eventual domination); in particular a sequence with 0≤uN≤cN−a for all N≥N0 converges to 0. By T.3(b), Nkexp(−cNa)→0 for a>0, c>0, k≥0. By T.4, for x≥0 the number ⌊x⌋+1 is a natural number in (x,x+1], and for every real x there is N0∈N with N>x for all N≥N0. By T.5, square roots are monotone and a+b≤a+b, ab=ab for a,b≥0; by T.6, exp(x)−1≤xexp(x) and exp(x)−1−x≤x2exp(x) for x≥0, and exp is nondecreasing with exp(−x)≤1 for x≥0. Limits of sums, products and scalar multiples are those of Arithmetic of Limits of Real Sequences; comparison and squeeze are claims 1 and 2 of Order Properties of Limits of Real Sequences; constant sequences converge to their value. Finally, T.3(e) gives uN→u and uN1/4→u1/4 when uN≥0 and uN→u, and T.3(f) gives exp(uN)→exp(u) when uN→u. Whenever finitely many natural numbers N0,N0′,… have been produced, "for all N beyond them" means for all N at least as large as the largest of them. Each of the finitely many thresholds produced in the proof of claim 1 is a natural number; Nc is taken to be the largest of them.
Proof of claim 1. (i) By T.4 with x=N1/16≥0, mN∈N and N1/16<mN≤N1/16+1≤2N1/16, since N1/16≥1.
(ii) By T.4 with x=N(Bs+1)≥0, RN∈N and N(Bs+1)<RN≤N(Bs+1)+1≤N(Bs+2), since 1≤N. Also RN>N(Bs+1)≥NBs and RN>N(Bs+1)≥N.
(iii) By T.4 with x=RNN−3/4>0, JN∈N and RNN−3/4<JN≤RNN−3/4+1. Hence μN=RN/JN<RN/(RNN−3/4)=N3/4, using N−3/4N3/4=1. Since RN≥N≥N3/4 we have RNN−3/4≥1, so JN≤2RNN−3/4 and μN≥N3/4/2. By eventual smallness of powers there is a threshold beyond which N−3/4≤41, i.e. N3/4≥4 and μN≥2. Next, dN=l(l−1)JN≥2JN>2RNN−3/4≥2NN−3/4=2N1/4≥N1/4, and JN≤RNN−3/4+1≤(Bs+2)NN−3/4+1=(Bs+2)N1/4+1≤(Bs+3)N1/4, whence dN≤l(l−1)(Bs+3)N1/4.
(iv) DN=N3/64≤N4/64=N1/16<mN. Hence mN+l(l−1)(DN+mN)≤mN(1+2l(l−1)) and AN≤CAmN≤2CAN1/16 by (i). As AN≥0, 0≤Λ1sAN<Λ1sAN+1=LN. Since LN≥1>0, T.4 gives MN∈N and LN<MN≤LN+1. Finally MN+2≤MN+3≤LN+4=Λ1sAN+5≤2Λ1sCAN1/16+5N1/16=CMN1/16, using N1/16≥1.
(v) By eventual smallness of powers (N−3/64≤41 beyond a threshold) we have DN=N3/64≥4 beyond it. Since N≥1, N−3/8≤N0=1 and N−1/8≤1, while all powers are positive; so 0<ηN≤1, 0<δN≤1, ζN>0. By T.4 with x=N1/4, θN∈N and N1/4<θN≤N1/4+1≤2N1/4.
(vi) By (i) and (iii), mN≤2N1/16 and μN/2≥N3/4/4, and 2N1/16<N3/4/4 holds as soon as 8N−11/16<1, since N3/4N−1/16=N11/16; this holds beyond a threshold by eventual smallness of powers.
(vii) By (iv), ε0,N=ΓAN/(Nb)≤(2ΓCA/b)N1/16N−1=(2ΓCA/b)N−15/16; by (v), 2θNε0,N≤(8ΓCA/b)N1/4N−15/16=(8ΓCA/b)N−11/16; by (iv), EˉN≤(4l~sΓ2CA2/b)N1/8N−1=(4l~sΓ2CA2/b)N−7/8; with CE=l~sB~(2ΓCA/b)2, EN⋆≤CENN−15/8=CEN−7/8 and ENch≤8CEN(2N1/4)2N−15/8=32CEN−3/8. By (i) and (iii), mN2/μN≤4N1/8/(N3/4/2)=8N−5/8≤8, so κ0,N≤1+4exp(8) (as exp is nondecreasing) and jˉN≤8(1+4exp(8))N−5/8; and κNmv=mN2N−1N3/8≤4N1/8−1+3/8=4N−1/2. Each of these seven majorants is a constant times a negative power of N, so by eventual smallness of powers each of the seven inequalities of (vii) holds beyond a threshold.
(viii) By (iii) and monotonicity of the square root, xN=μN1/2N1/32≤(N3/4)1/2N1/32=N3/8N1/32=N13/32. Hence, by (i), mN(xN+mN)≤2N1/16(N13/32+2N1/16)=2N15/32+4N1/8≤6N15/32, since N1/8≤N15/32. On the other hand δNμN/2≥N−1/8N3/4/4=N5/8/4. Now 6N15/32≤N5/8/4 holds as soon as 24N−5/32≤1, since N5/8N−15/32=N5/32; this holds beyond a threshold. This completes the proof of claim 1, with Nc the largest of the thresholds.
Proof of claim 2. Let k>0 and 0≤x≤x′. Then x2≤x′2 (Monotonicity of Squaring on the Nonnegative Elements of an Ordered Field), so ϖk(x)≤x2/(4k)≤x′2/(4k) and ϖk(x)≤x/2≤x′/2; hence ϖk(x)≤ϖk(x′), the smaller of the two bounds. Let n≥0, N∈N and y=(n+2)1/2N1/32. Then y2=(n+2)N1/16, so y2/(4(n+2))=N1/16/4≥N1/32/4, and y/2≥2N1/32/2≥N1/32/4 because (n+2)1/2≥2 by monotonicity of the square root and 2/2≥1/4 (as 2≥1/2, since 2≥1/4); hence ϖn+2(y)≥N1/32/4. Now let N≥Nc. First, xN2=μNN1/16 gives xN2/(4μN)=N1/16/4≥N1/32/4, and μN≥2≥1 gives μN1/2≥1 and xN/2≥N1/32/2; so ϖμN(xN)≥N1/32/4. Second, by claim 1(vi), μN−mN≥μN/2≥0, so by monotonicity ϖμN(μN−mN)≥ϖμN(μN/2)=(μN/16)∧(μN/4)=μN/16≥N3/4/32. Third, by claim 1(v), DN≥4, so DN−2≥DN/2≥0, and by claim 1(iv), MN+2≤CMN1/16; hence
the last step because CM≥5 gives cw≤801. Thus ϖMN+2(DN−2)≥cwN1/32.
Proof of claim 3. First, for every N∈N, all quantities of the statement are well-defined nonnegative real numbers: they are formed from nonnegative data by sums, products, quotients by positive numbers, square roots of nonnegative numbers and exponentials, together with the differences exp(u)−1≥0 for u≥0 (exp being nondecreasing with exp(0)=1) and exp(u)−1−u≥0 for u≥0 (T.6), the product κ0,N−1=2μNmN2exp(mN2/μN)≥0 of nonnegative numbers, and, inside gN, the arguments μN−mN and DN−2 of ϖ, which are nonnegative whenever the formula for gN is read; in particular JN≥0 and IN≥0. Throughout the rest of this proof, N≥Nc, so that all statements of claims 1 and 2 are available; every bound below is of the form "0≤uN≤ (constant)⋅N−a" or "0≤uN≤ (constant)⋅Nkexp(−cNa)", and the corresponding limit uN→0 then follows from eventual domination together with cN−a→0 or Nkexp(−cNa)→0. We also use the bounds wN≤2Λl(l−1)(Bs+2)NN−1/16=CwN15/16 with Cw=2Λl(l−1)(Bs+2) (from claim 1(i),(ii)), hence wN2/N≤Cw2N7/8, and αN≤CαN1/8 with Cα=(2l(l−1)(Bs+3))1/2c0Φˉ2 (from claim 1(iii) and monotonicity of the square root, (N1/4)1/2=N1/8).
(a)εS,N and εctl,N are constant multiples of N−1/4, so they converge to 0. The bounds recorded in the proof of claim 1(vii) give ε0,N→0 and EˉN→0. By T.6 and EˉN≤1, cN=exp(EˉN)−1≤EˉNexp(EˉN)≤exp(1)EˉN, so cN→0. By EN⋆≤1 and T.6, exp(9EN⋆)−1≤9EN⋆exp(9), so, writing t3/2=tt1/2 for t≥0, using (EN⋆)2=EN⋆(EN⋆)1/2(EN⋆)1/2≤(EN⋆)3/2 (as (EN⋆)1/2≤1 by monotonicity of the square root) and ab=ab,
where (CEN−7/8)3/2=CE3/2N−7/8N−7/16 by multiplicativity of the square root and (N−7/8)1/2=N−7/16, and monotonicity of t↦t3/2 on [0,∞) follows from that of t↦t and t↦t1/2; so eN⋆→0. Next, 0≤κ0,N−1=2μNmN2exp(mN2/μN)≤4N−5/8exp(8) by the bound mN2/μN≤8N−5/8≤8 of claim 1(vii); so κ0,N→1, and jˉN≤8(1+4exp(8))N−5/8 gives jˉN→0. Since jˉN≤1, (1+jˉN)1/2+1≤2+1, so jN⋆≤(2+1)jˉN1/2≤(2+1)(8(1+4exp(8)))1/2N−5/16 by monotonicity of the square root and (N−5/8)1/2=N−5/16; so jN⋆→0.
For ΠˉN: by claim 2 and monotonicity of exp, exp(−ϖμN(xN))≤exp(−N1/32/4); by claim 1(v),(vii), θNδN/2≥N1/4N−1/8/2=N1/8/2≥N1/32/4 and ENch≤1, so exp(−θNδN/2+ENch)≤exp(1)exp(−N1/32/4). Hence, with claim 1(iii),
with Cg=l(l−1)((Bs+3)+2(Bs+3)CM) (using (Bs+2)N+1≤(Bs+3)N and NN1/16≤N2); both terms converge to 0 by T.3(b), so gN→0 by the sum law and squeeze.
For eF,N: its first summand is a constant multiple of N−1/4; in the second, by claim 1(iii),(iv), AN/μN≤2CAN1/16/(N3/4/2)=4CAN−11/16≤4CA, so 3+2(Λ1sAN+μN)/μN≤5+8Λ1sCA and the second summand is at most 2Λl(l−1)(5+8Λ1sCA)N−1/4 (as μN/N≤N−1/4). Hence eF,N→0. For ϵψ,N: wN/N≤CwN−1/16, and DN+Λ2sAN2/N≤N3/64+4Λ2sCA2N1/8−1≤(1+4Λ2sCA2)N3/64, so the middle summand inside the bracket is at most 2l(l−1)Cw(1+4Λ2sCA2)N−1/64, since N−1/16N3/64=N−1/64; the third summand is a constant multiple of N−1/4. Hence each of the three summands converges to 0, and by the sum and scalar-multiple laws ϵψ,N→0. Then κN→0 by the sum and product laws, as κN is a polynomial expression in εS,N and ϵψ,N (both null) with constant coefficients and no constant term. For QN: ζN→0, so (1+ζN)(Q+l~sκN)→Q by the sum and product laws; and, using claim 1(iv) and 1+1/ζN=1+N1/2≤2N1/2,
For the bad term, put bN=2dNwN2BN/N. By claim 1(iii) and the bound on wN2/N, 2dNwN2/N≤2l(l−1)(Bs+3)Cw2N9/8=CbN9/8. Since jˉN≤1 and cN≤exp(1)EˉN≤exp(1), we have (1+jˉN)1/2≤2 and, by monotonicity of the square root and ab=ab, (cNΠˉN)1/2≤exp(1)1/2ΠˉN1/2, so
where dN3/2=dNdN1/2. Write ΠˉN≤CΠN1/4exp(−N1/32/4) for the bound obtained above, with CΠ=(1+exp(1))l(l−1)(Bs+3), and note dN≤CdN1/4 with Cd=l(l−1)(Bs+3). Since exp(−u)=exp(−u/2) for real u (the right-hand side is positive with square exp(−u)), monotonicity and multiplicativity of the square root give ΠˉN1/2≤CΠ1/2N1/8exp(−N1/32/8) and gN1/2≤Cg1/2(N1/8exp(−N3/4/64)+Nexp(−cwN1/32/2)) (using a+b≤a+b). Multiplying out, bN≤CbN9/8BN is bounded by a finite sum of terms of the form (constant)⋅Nkexp(−cNa) with k≥0, c>0, a>0; explicitly, the five terms are bounded by
Each of these converges to 0 by T.3(b), so bN→0 by the sum law and squeeze.
Finally, by the bound on eN⋆ obtained above, NwN2eN⋆≤Cw2CeCE3/2N7/8−21/16=Cw2CeCE3/2N−7/16→0. Next NwN2EˉN(N−1/2+c⋆N−1)≤Cw2(4l~sΓ2CA2/b)(1+c⋆)N7/8−7/8−1/2→0, using N−1≤N−1/2; and NwN2cNjN⋆≤Cw2exp(1)(4l~sΓ2CA2/b)(2+1)(8(1+4exp(8)))1/2N7/8−7/8−5/16→0. Since δN→0, κ0,NP→P, QN→Q and bN→0, the sum and product laws give JN→1⋅(P+Q+0)+0=P+Q.
(b)e2,N is a sum of constant multiples of N−1/2, εS,N and εctl,N, with no constant term, so e2,N→0 by the sum and scalar-multiple laws. For e3,N: put Cclk=Λ1s(Cflw+1)+CLip(TCctl)1/2, so that w1,N=CclkNN−1/4=CclkN3/4, while w2,N=μN≤N3/4; hence wi,N+3≤(Cclk+4)N3/4 and wi,N+4≤(Cclk+5)N3/4 for i∈{1,2}, using 1≤N3/4. By monotonicity of the square root, (wi,N+3)1/2≤(Cclk+4)1/2N3/8. Next, RN≥1 gives 8(4096+17RN4)≤8⋅4113RN4≤144RN4 (as 8⋅4113=32904≤38416=144), so (8(4096+17RN4))1/4≤14RN≤14(Bs+2)N by monotonicity of the fourth root; and (2(RN+1)(wi,N+4))1/4≤(4(Bs+2)(Cclk+5))1/4(NN3/4)1/4=(4(Bs+2)(Cclk+5))1/4N7/16, using RN+1≤2RN. Therefore
and multiplying by c0l(l−1)(2+H)N−1/2 gives e3,N≤C3(N−3/32+N−1/2+N15/16exp(−N1/32/16)) with C3=c0l(l−1)(2+H)max{2(Cclk+4)1/2,4,28(Bs+2)(4(Bs+2)(Cclk+5))1/4} (the largest of three reals), since N3/8+1/32−1/2=N−3/32 and N1+7/16−1/2=N15/16; each of the three terms converges to 0, so e3,N→0. Next, e4,N=ηN1/2αN≤N−3/16CαN1/8=CαN−1/16→0. For e5,N: since μN≥1, 3μN2+μN≤4μN2, so kN≤αN(4μN2)1/4=2αNμN1/2≤2CαN1/8N3/8=2CαN1/2 (using (4μN2)1/2=2μN and (2μN)1/2=2μN1/2), whence kN/N≤2Cα and
Since gN→0 and N−1/2+c⋆N−1→0, T.3(e) gives gN1/4→0 and (N−1/2+c⋆N−1)1/4→0, so the right-hand side converges to 0 by the sum and scalar-multiple laws, and the squeeze gives e5,N→0. Finally einj,N≤2l(l−1)c0ΛΦˉ2(ΛEs+1)N−1/4 by μN≤N3/4, and aN≤22c0Φˉ2N1/16N−1/2=22c0Φˉ2N−7/16 by claim 1(i); both converge to 0.
(c) By the bound recorded in the proof of claim 1(vii), κNmv≤4N−1/2, and by claim 1(vii) itself κNmv≤1; so by T.6, exp(κNmv)−1−κNmv≤(κNmv)2exp(1), and by monotonicity and multiplicativity of the square root (exp(κNmv)−1−κNmv)1/2≤exp(1)1/2κNmv≤4exp(1)1/2N−1/2. Hence the second summand inside the square defining IN satisfies
Since JN≥0 and JN→P+Q by (a), T.3(e) gives JN1/2→(P+Q)1/2; by the sum law the base of the square converges to (P+Q)1/2, and by the product law IN→((P+Q)1/2)2=P+Q.
Proof of claim 4. Let ϵ>0. By claim 3(b) and the sum law, e2,N+e3,N+e4,N+e5,N→0; by claim 3(b), einj,N→0 and aN→0; by claim 3(a), gN→0; by claim 3(c), IN→P+Q. Applying T.3(d) to each of these five sequences with the strict upper bounds ϵ (for the first three and the fifth; their limits are 0<ϵ) and P+Q+ϵ (for the fourth) yields five thresholds beyond which the respective strict inequalities, and hence the stated weak inequalities, hold; let Nsc be the largest of these thresholds and of Nc. ■