\import Algebra.Group
\import Algebra.Meta
\import Algebra.Monoid
\import Algebra.Ordered
\import Arith.Rat
\import Arith.Real
\import Function.Meta
\import Logic
\import Logic.Meta
\import Meta
\import Operations
\import Order.Lattice
\import Order.LinearOrder
\import Order.PartialOrder
\import Order.StrictOrder
\import Paths
\import Paths.Meta
\import Set.Filter
\import Set.Subset
\import Topology.CoverSpace
\import Topology.CoverSpace.Complete
\import Topology.CoverSpace.Product
\import Topology.MetricSpace
\import Topology.NormedAbGroup
\import Topology.RatherBelow
\import Topology.UniformSpace
\open LinearlyOrderedAbGroup
\open RealNormed
\open ProductCoverSpace
\open OrderedAbGroup

\instance RatNormed : NormedAbGroup
| AbGroup => RatField
| norm a => abs a
| norm_zro => pmap Real.fromRat abs_zro
| norm_negative => pmap Real.fromRat abs_negative
| norm_+ => transportInv (_ <=) RealAbGroup.+-rat $rat_real_<=.1 abs_+ | norm-ext p => abs_zro-ext$ Real.fromRat-inj p

\instance RealNormed : CompleteNormedAbGroup
| NormedAbGroup => RealNormedAbGroup
| isComplete => dense-complete (rat_real.dense, rat_real.embedding->coverEmbedding (rat_real.dense->uniformEmbedding rat_real.dense).2)
\lam F => inP (fromCF F, \lam {U} => \case <=<-ball __ \with {
| inP (eps,eps>0,p) =>
\let | x => fromCF F
| (inP (a, x-eps<a, inP (y1,eps1,eps1>0,Fy1,a<y1-eps1))) => (real_<-rat-char {x - eps} {x}).1 $transport (_ <) zro-right$ <_+-right x $RealAbGroup.positive_negative eps>0 | (inP (b, inP (y2,eps2,eps2>0,Fy2,y2+eps2<b), b<x+eps)) => (real_<-rat-char {x} {x + eps}).1$ transport {Real} (< _) zro-right $<_+-right x eps>0 \in filter-mono ((later \lam {z} (|y1-z|<eps1,|y2-z|<eps2) => abs_-_< (RealAbGroup.<-diff-left$ real_<_U.2 x-eps<a <∘ real_<_L.2 (linarith $abs>=id <∘r real_<_L.1 (transport (< _) norm-dist |y1-z|<eps1))) (RealAbGroup.<-diff-mid-conv$ rewrite +-comm $real_<_L.2 (linarith$ RatField.abs>=neg {y2 - z} <∘r real_<_L.1 (transport (< _) norm-dist |y2-z|<eps2)) <∘ real_<_L.2 b<x+eps)) <=∘ ^-1_<= rat_real p) (filter-meet Fy1 Fy2)
})
\where {
\func RealNormedAbGroup : NormedAbGroup \cowith
| AbGroup => RealAbGroup
| norm => abs
| norm_zro => abs_zro
| norm_negative => abs_negative
| norm_+ => abs_+
| norm-ext => abs_zro-ext

\func fromCF (F : RegularCauchyFilter RatNormed) : Real \cowith
| L a => ∃ (x eps : Rat) (0 < eps) (F (OBall eps x)) (a < x - eps)
| L-inh => \case cauchyFilter-metric-char.1 F.isCauchyFilter {1} RealAbGroup.zro<ide \with {
| inP (x,FB) => inP (x - 2, inP (x, 1, idp, FB, linarith))
}
| L-closed (inP (x,eps,eps>0,FB,q<x-eps)) q'<q => inP (x, eps, eps>0, FB, q'<q <∘ q<x-eps)
| L-rounded {a} (inP (x,eps,eps>0,FB,a<x-eps)) => inP (RatField.mid a (x - eps), inP (x, eps, eps>0, FB, RatField.mid<right a<x-eps), RatField.mid>left a<x-eps)
| U b => ∃ (x eps : Rat) (0 < eps) (F (OBall eps x)) (x + eps < b)
| U-inh => \case cauchyFilter-metric-char.1 F.isCauchyFilter {1} RealAbGroup.zro<ide \with {
| inP (x,FB) => inP (x + 2, inP (x, 1, idp, FB, linarith))
}
| U-closed (inP (x,eps,eps>0,FB,x+eps<q)) q<q' => inP (x, eps, eps>0, FB, x+eps<q <∘ q<q')
| U-rounded {a} (inP (x,eps,eps>0,FB,x+eps<a)) => inP (RatField.mid (x + eps) a, inP (x, eps, eps>0, FB, RatField.mid>left x+eps<a), RatField.mid<right x+eps<a)
| LU-disjoint (inP (x,eps,eps>0,Feps,q<x-eps)) (inP (y,delta,delta>0,Fdelta,x+eps<q)) => \case F.isProper (F.filter-meet Feps Fdelta) \with {
| inP (z,(|x-z|<eps,|y-z|<delta)) =>
\have | t => abs>=id <∘r real_<_L.1 (transport (< _) norm-dist |x-z|<eps)
| s => RatField.abs>=neg {y - z} <∘r real_<_L.1 (transport (< _) norm-dist |y-z|<delta)
\in linarith
}
| LU-focus eps eps>0 => \case cauchyFilter-metric-char.1 F.isCauchyFilter {eps * ratio 1 4} (real_<_L.2 linarith) \with {
| inP (x,FB) => inP (x - eps * ratio 1 2, inP (x, _, linarith, FB, linarith), inP (x, _, linarith, FB, linarith))
}
}

\func rat_real : NormedIsometricMap RatNormed RealNormedAbGroup Real.fromRat \cowith
| func-+ => inv RealAbGroup.+-rat
| func-norm-isometry => inv rat_real_abs
\where {
\lemma dense : rat_real.IsDense
=> \lam {y} {U} Uo Uy => \case (dist_open {RealNormedAbGroup} {U}).1 Uo Uy \with {
| inP (eps,eps>0,p) => \case real_<-rat-char.1 $transport (< _) zro-right$ <_+-right y eps>0 \with {
| inP (x,y<x,x<y+eps) => inP (x, inP (x, idp), p $unfold OBall$ rewrite norm-dist $abs_-_< (transport (_ <) negative-right (RealAbGroup.<_+-left _$ real_<_U.2 y<x) <∘ eps>0) $transport2 (<) +-comm (inv +-assoc *> pmap (+ _) negative-left *> zro-left)$ <_+-right (negative y) $real_<_L.2 x<y+eps) } } \lemma dense-coverEmbedding : CoverMap.IsDenseEmbedding {rat_real} => (dense, rat_real.embedding->coverEmbedding (rat_real.dense->uniformEmbedding dense).2) } \func open-rat-int (a b : Rat) : Set Real => \lam (x : Real) => \Sigma (x.L a) (x.U b) \lemma dense-lift-real-char {X Y : CoverSpace} {f : CoverMap X Y} (fd : f.IsDenseEmbedding) {g : CoverMap X RealNormed} (y : Y) (a b : Rat) : open-rat-int a b (dense-lift f fd g y) <-> ∃ (a' b' : Rat) (a < a') (b' < b) (V : Set Y) (f ^-1 V ⊆ g ^-1 open-rat-int a' b') (single y <=< V) => (\lam (a<z,z<b) => \case L-rounded a<z, U-rounded z<b \with { | inP (a',a'<z,a<a'), inP (b',z<b',b'<b) => \case (dense-lift-neighborhood fd y (open-rat-int a' b')).1 (point_<=< a'<z z<b') \with { | inP (W,W<=<a'b',V,q,y<=<V) => inP (a', b', a<a', b'<b, V, q <=∘ <=<_<= (<=<_^-1 W<=<a'b'), y<=<V) } }, \lam (inP (a',b',a<a',b'<b,V,h,y<=<V)) => <=<_<= ((dense-lift-neighborhood fd y (\lam x => open-rat-int a b x)).2$ inP (open-rat-int a' b', <=<_open-rat-int a<a' b'<b, V, h, y<=<V)) idp)
\where {
\open ClosurePrecoverSpace

\lemma makeRealCover (eps : Rat) (eps>0 : 0 < eps) : RealNormed.isCauchy \lam U => ∃ (a : Rat) (U = open-rat-int a (a + eps))
=> RealNormed.makeCauchy $inP (eps * ratio 1 4, real_<_L.2 linarith, \lam x => later \case (real_<-rat-char {x - eps * ratio 1 2} {x - eps * ratio 1 4}).1$ <_+-right x $RealAbGroup.negative_<$ real_<_L.2 linarith \with {
| inP (a,x-eps/2<a,a<x-eps/4) => inP (_, inP (a, idp), \lam d => (
real_<_L.1 $real_<_L.2 a<x-eps/4 <∘ RealAbGroup.<-diff-left (abs>=id <∘r (rewrite norm-dist in d)), real_<_U.1$ RealAbGroup.<-diff-mid (simplify in abs>=neg <∘r (rewrite norm-dist in d)) <∘
<_+-right _ (RealAbGroup.<-diff-mid (real_<_U.2 x-eps/2<a)) <∘ rewrite (RealAbGroup.+-rat,RealAbGroup.+-rat) (real_<_L.2 linarith)))
})

\lemma <=<_open-rat-int {a b a' b' : Rat} (a<a' : a < a') (b'<b : b' < b) : open-rat-int a' b' <=< open-rat-int a b
=> closure-subset (makeRealCover ((a' - a) ∧ (b - b')) $LinearOrder.<_meet-univ linarith linarith) \lam {U} (inP (c,p)) => rewrite p$ later \lam (e : Real, ((a'<e,e<b'),(c<e,e<c+eps))) (c<x,x<c+eps) => (L-closed c<x $linarith (e.LU-less a'<e e<c+eps <∘l RatField.<=_+ <=-refl meet-left), U-closed x<c+eps$ RatField.<=_+ <=-refl meet-right <∘r linarith (e.LU-less c<e e<b'))

\lemma point_<=< {x : Real} {a b : Rat} (a<x : x.L a) (x<b : x.U b) : single x <=< open-rat-int a b
=> \case x.L-rounded a<x, x.U-rounded x<b \with {
| inP (a',a'<x,a<a'), inP (b',x<b',b'<b) => <=<-right (later \lam p => rewriteI p (a'<x,x<b')) (<=<_open-rat-int a<a' b'<b)
}
}

\lemma <=<-open-int {x : Real} {U : Set Real} (p : single x <=< U) : ∃ (a b : Rat) (x.L a) (x.U b) ∀ (y : Real) (y.L a -> y.U b -> U y)
=> \case <=<-ball p \with {
| inP (eps,eps>0,q) => \case (real_<-rat-char {x - eps} {x}).1 $transport (_ <) zro-right$ <_+-right x $RealAbGroup.positive_negative eps>0, (real_<-rat-char {x} {x + eps}).1$ transport (< _) zro-right $<_+-right x eps>0 \with { | inP (a,x-eps<a,a<x), inP (b,x<b,b<x+eps) => inP (a, b, a<x, x<b, \lam y a<y y<b => q$ transportInv (< _) norm-dist $abs_-_< (RealAbGroup.<-diff-left$ real_<_U.2 x-eps<a <∘ real_<_L.2 a<y) $RealAbGroup.<-diff-mid-conv$ rewrite +-comm $real_<_U.2 y<b <∘ real_<_L.2 b<x+eps) } } \func real-lift2 {X : CompleteCoverSpace} (f : CoverMap (RatNormed ⨯ RatNormed) X) : CoverMap (RealNormed ⨯ RealNormed) X => dense-lift (prod rat_real rat_real) (prod.isDenseEmbedding rat_real.dense-coverEmbedding rat_real.dense-coverEmbedding) f \lemma real-lift2-char {f : CoverMap (RatNormed ⨯ RatNormed) RealNormed} {x y : Real} (a b : Rat) : open-rat-int a b (real-lift2 f (x,y)) <-> ∃ (a' b' c1 d1 c2 d2 : Rat) (a < a') (b' < b) (x.L c1) (x.U d1) (y.L c2) (y.U d2) (\Pi {x y : Rat} -> \Sigma (c1 < x) (x < d1) -> \Sigma (c2 < y) (y < d2) -> open-rat-int a' b' (f (x,y))) => <->trans (dense-lift-real-char {RatNormed ⨯ RatNormed} {_} {prod rat_real rat_real} (prod.isDenseEmbedding rat_real.dense-coverEmbedding rat_real.dense-coverEmbedding) (x,y) a b)$ later
(\lam (inP (a',b',a<a',b'<b,V,q,xy<=<V)) => \case prod-neighborhood.1 xy<=<V \with {
| inP (U,V,x<=<U,y<=<V,h) => \case <=<-open-int x<=<U, <=<-open-int y<=<V \with {
| inP (c1,d1,c1<x,x<d1,p1), inP (c2,d2,c2<y,y<d2,p2) => inP (a', b', c1, d1, c2, d2, a<a', b'<b, c1<x, x<d1, c2<y, y<d2, \lam {x'} {y'} (c1<x',x'<d1) (c2<y',y'<d2) => q $h (p1 x' c1<x' x'<d1) (p2 y' c2<y' y'<d2)) } }, \lam (inP (a',b',c1,d1,c2,d2,a<a',b'<b,c1<x,x<d1,c2<y,y<d2,q)) => inP (a', b', a<a', b'<b, \lam z => \Sigma (open-rat-int c1 d1 z.1) (open-rat-int c2 d2 z.2), \lam s => q s.1 s.2, RatherBelow.<=<_meet-same (<=<-right (later \lam s => pmap __.1 s)$ <=<_^-1 {_} {_} {proj1} $dense-lift-real-char.point_<=< c1<x x<d1) (<=<-right (later \lam s => pmap __.2 s)$ <=<_^-1 {_} {_} {proj2} \$ dense-lift-real-char.point_<=< c2<y y<d2)))`