author  paulson 
Sun, 15 Feb 2004 10:46:37 +0100  
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permissions  rwrr 
5078  1 
(* Title : RComplete.thy 
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ID : $Id$ 
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Author : Jacques D. Fleuriot 
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Copyright : 1998 University of Cambridge 

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Description : Completeness theorems for positive 

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reals and reals 

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*) 

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header{*Completeness Theorems for Positive Reals and Reals.*} 
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theory RComplete = Lubs + RealDef: 
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lemma real_sum_of_halves: "x/2 + x/2 = (x::real)" 
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by simp 
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subsection{*Completeness of Reals by Supremum Property of type @{typ preal}*} 
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(*a few lemmas*) 
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lemma real_sup_lemma1: 
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"\<forall>x \<in> P. 0 < x ==> 
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((\<exists>x \<in> P. y < x) = (\<exists>X. real_of_preal X \<in> P & y < real_of_preal X))" 
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by (blast dest!: bspec real_gt_zero_preal_Ex [THEN iffD1]) 
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lemma real_sup_lemma2: 
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"[ \<forall>x \<in> P. 0 < x; a \<in> P; \<forall>x \<in> P. x < y ] 
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==> (\<exists>X. X\<in> {w. real_of_preal w \<in> P}) & 
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(\<exists>Y. \<forall>X\<in> {w. real_of_preal w \<in> P}. X < Y)" 
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apply (rule conjI) 
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apply (blast dest: bspec real_gt_zero_preal_Ex [THEN iffD1], auto) 
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apply (drule bspec, assumption) 
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apply (frule bspec, assumption) 
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apply (drule order_less_trans, assumption) 
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apply (drule real_gt_zero_preal_Ex [THEN iffD1], force) 
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done 
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(* 
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Completeness of Positive Reals 
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*) 
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(** 
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Supremum property for the set of positive reals 
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FIXME: long proof  should be improved 
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**) 
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(*Let P be a nonempty set of positive reals, with an upper bound y. 
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Then P has a least upper bound (written S). 
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FIXME: Can the premise be weakened to \<forall>x \<in> P. x\<le> y ??*) 
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lemma posreal_complete: "[ \<forall>x \<in> P. (0::real) < x; \<exists>x. x \<in> P; \<exists>y. \<forall>x \<in> P. x<y ] 
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==> (\<exists>S. \<forall>y. (\<exists>x \<in> P. y < x) = (y < S))" 
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apply (rule_tac x = "real_of_preal (psup ({w. real_of_preal w \<in> P}))" in exI) 
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apply clarify 
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apply (case_tac "0 < ya", auto) 
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apply (frule real_sup_lemma2, assumption+) 
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apply (drule real_gt_zero_preal_Ex [THEN iffD1]) 
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apply (drule_tac [3] real_less_all_real2, auto) 
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apply (rule preal_complete [THEN iffD1]) 
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apply (auto intro: order_less_imp_le) 
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apply (frule real_gt_preal_preal_Ex, force) 
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(* second part *) 
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apply (rule real_sup_lemma1 [THEN iffD2], assumption) 
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apply (auto dest!: real_less_all_real2 real_gt_zero_preal_Ex [THEN iffD1]) 
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apply (frule_tac [2] real_sup_lemma2) 
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apply (frule real_sup_lemma2, assumption+, clarify) 
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apply (rule preal_complete [THEN iffD2, THEN bexE]) 
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prefer 3 apply blast 
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apply (blast intro!: order_less_imp_le)+ 
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done 
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(* 
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Completeness properties using isUb, isLub etc. 
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*) 
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lemma real_isLub_unique: "[ isLub R S x; isLub R S y ] ==> x = (y::real)" 
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apply (frule isLub_isUb) 
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apply (frule_tac x = y in isLub_isUb) 
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apply (blast intro!: real_le_anti_sym dest!: isLub_le_isUb) 
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done 
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lemma real_order_restrict: "[ (x::real) <=* S'; S <= S' ] ==> x <=* S" 
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by (unfold setle_def setge_def, blast) 
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(* 
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Completeness theorem for the positive reals(again) 
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*) 
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lemma posreals_complete: 
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"[ \<forall>x \<in>S. 0 < x; 
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\<exists>x. x \<in>S; 
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\<exists>u. isUb (UNIV::real set) S u 
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] ==> \<exists>t. isLub (UNIV::real set) S t" 
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apply (rule_tac x = "real_of_preal (psup ({w. real_of_preal w \<in> S}))" in exI) 
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apply (auto simp add: isLub_def leastP_def isUb_def) 
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apply (auto intro!: setleI setgeI dest!: real_gt_zero_preal_Ex [THEN iffD1]) 
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apply (frule_tac x = y in bspec, assumption) 
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apply (drule real_gt_zero_preal_Ex [THEN iffD1]) 
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apply (auto simp add: real_of_preal_le_iff) 
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apply (frule_tac y = "real_of_preal ya" in setleD, assumption) 
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apply (frule real_ge_preal_preal_Ex, safe) 
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apply (blast intro!: preal_psup_le dest!: setleD intro: real_of_preal_le_iff [THEN iffD1]) 
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apply (frule_tac x = x in bspec, assumption) 
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apply (frule isUbD2) 
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apply (drule real_gt_zero_preal_Ex [THEN iffD1]) 
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apply (auto dest!: isUbD real_ge_preal_preal_Ex simp add: real_of_preal_le_iff) 
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apply (blast dest!: setleD intro!: psup_le_ub intro: real_of_preal_le_iff [THEN iffD1]) 
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done 
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5078  108 

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(* 
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Lemmas 
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*) 
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lemma real_sup_lemma3: "\<forall>y \<in> {z. \<exists>x \<in> P. z = x + (xa) + 1} Int {x. 0 < x}. 0 < y" 
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by auto 
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lemma lemma_le_swap2: "(xa <= S + X + (Z)) = (xa + (X) + Z <= (S::real))" 
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by auto 
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lemma lemma_real_complete2b: "[ (x::real) + (X) + 1 <= S; xa <= x ] ==> xa <= S + X + ( 1)" 
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by arith 
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(* 
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reals Completeness (again!) 
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*) 
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lemma reals_complete: "[ \<exists>X. X \<in>S; \<exists>Y. isUb (UNIV::real set) S Y ] 
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==> \<exists>t. isLub (UNIV :: real set) S t" 
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apply safe 
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apply (subgoal_tac "\<exists>u. u\<in> {z. \<exists>x \<in>S. z = x + (X) + 1} Int {x. 0 < x}") 
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128 
apply (subgoal_tac "isUb (UNIV::real set) ({z. \<exists>x \<in>S. z = x + (X) + 1} Int {x. 0 < x}) (Y + (X) + 1) ") 
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129 
apply (cut_tac P = S and xa = X in real_sup_lemma3) 
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130 
apply (frule posreals_complete [OF _ _ exI], blast, blast, safe) 
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131 
apply (rule_tac x = "t + X + ( 1) " in exI) 
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132 
apply (rule isLubI2) 
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133 
apply (rule_tac [2] setgeI, safe) 
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134 
apply (subgoal_tac [2] "isUb (UNIV:: real set) ({z. \<exists>x \<in>S. z = x + (X) + 1} Int {x. 0 < x}) (y + (X) + 1) ") 
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135 
apply (drule_tac [2] y = " (y + ( X) + 1) " in isLub_le_isUb) 
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136 
prefer 2 apply assumption 
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137 
prefer 2 
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138 
apply arith 
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139 
apply (rule setleI [THEN isUbI], safe) 
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140 
apply (rule_tac x = x and y = y in linorder_cases) 
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141 
apply (subst lemma_le_swap2) 
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142 
apply (frule isLubD2) 
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143 
prefer 2 apply assumption 
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144 
apply safe 
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145 
apply blast 
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146 
apply arith 
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147 
apply (subst lemma_le_swap2) 
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148 
apply (frule isLubD2) 
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149 
prefer 2 apply assumption 
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150 
apply blast 
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151 
apply (rule lemma_real_complete2b) 
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152 
apply (erule_tac [2] order_less_imp_le) 
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153 
apply (blast intro!: isLubD2, blast) 
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154 
apply (simp (no_asm_use) add: real_add_assoc) 
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155 
apply (blast dest: isUbD intro!: setleI [THEN isUbI] intro: add_right_mono) 
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156 
apply (blast dest: isUbD intro!: setleI [THEN isUbI] intro: add_right_mono, auto) 
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157 
done 
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158 

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159 

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160 
subsection{*Corollary: the Archimedean Property of the Reals*} 
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161 

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162 
lemma reals_Archimedean: "0 < x ==> \<exists>n. inverse (real(Suc n)) < x" 
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163 
apply (rule ccontr) 
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164 
apply (subgoal_tac "\<forall>n. x * real (Suc n) <= 1") 
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165 
prefer 2 
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166 
apply (simp add: linorder_not_less inverse_eq_divide, clarify) 
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167 
apply (drule_tac x = n in spec) 
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168 
apply (drule_tac c = "real (Suc n)" in mult_right_mono) 
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169 
apply (rule real_of_nat_ge_zero) 
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170 
apply (simp add: real_of_nat_Suc_gt_zero [THEN real_not_refl2, THEN not_sym] real_mult_commute) 
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171 
apply (subgoal_tac "isUb (UNIV::real set) {z. \<exists>n. z = x* (real (Suc n))} 1") 
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172 
apply (subgoal_tac "\<exists>X. X \<in> {z. \<exists>n. z = x* (real (Suc n))}") 
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173 
apply (drule reals_complete) 
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174 
apply (auto intro: isUbI setleI) 
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175 
apply (subgoal_tac "\<forall>m. x* (real (Suc m)) <= t") 
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176 
apply (simp add: real_of_nat_Suc right_distrib) 
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177 
prefer 2 apply (blast intro: isLubD2) 
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178 
apply (simp add: le_diff_eq [symmetric] real_diff_def) 
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179 
apply (subgoal_tac "isUb (UNIV::real set) {z. \<exists>n. z = x* (real (Suc n))} (t + (x))") 
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180 
prefer 2 apply (blast intro!: isUbI setleI) 
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181 
apply (drule_tac y = "t+ (x) " in isLub_le_isUb) 
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182 
apply (auto simp add: real_of_nat_Suc right_distrib) 
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183 
done 
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184 

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185 
(*There must be other proofs, e.g. Suc of the largest integer in the 
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186 
cut representing x*) 
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187 
lemma reals_Archimedean2: "\<exists>n. (x::real) < real (n::nat)" 
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188 
apply (rule_tac x = x and y = 0 in linorder_cases) 
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189 
apply (rule_tac x = 0 in exI) 
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190 
apply (rule_tac [2] x = 1 in exI) 
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191 
apply (auto elim: order_less_trans simp add: real_of_nat_one) 
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192 
apply (frule positive_imp_inverse_positive [THEN reals_Archimedean], safe) 
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193 
apply (rule_tac x = "Suc n" in exI) 
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194 
apply (frule_tac b = "inverse x" in mult_strict_right_mono, auto) 
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195 
done 
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196 

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197 
lemma reals_Archimedean3: "0 < x ==> \<forall>y. \<exists>(n::nat). y < real n * x" 
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198 
apply safe 
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199 
apply (cut_tac x = "y*inverse (x) " in reals_Archimedean2) 
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200 
apply safe 
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201 
apply (frule_tac a = "y * inverse x" in mult_strict_right_mono) 
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202 
apply (auto simp add: mult_assoc real_of_nat_def) 
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203 
done 
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204 

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205 
ML 
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206 
{* 
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207 
val real_sum_of_halves = thm "real_sum_of_halves"; 
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208 
val posreal_complete = thm "posreal_complete"; 
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209 
val real_isLub_unique = thm "real_isLub_unique"; 
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210 
val real_order_restrict = thm "real_order_restrict"; 
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211 
val posreals_complete = thm "posreals_complete"; 
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212 
val reals_complete = thm "reals_complete"; 
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213 
val reals_Archimedean = thm "reals_Archimedean"; 
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214 
val reals_Archimedean2 = thm "reals_Archimedean2"; 
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215 
val reals_Archimedean3 = thm "reals_Archimedean3"; 
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216 
*} 
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217 

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218 
end 
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219 

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220 

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221 