meng_scaff[T: TYPE]: THEORY
BEGIN
IMPORTING meng_scaff_defs[T], sep_set_lems[T], min_lem
G,MM: VAR graph[T]
v,s,t,w1,w2: VAR T
W: VAR finite_set[T]
p: VAR prewalk
i: VAR nat
P: VAR pred[T]
ps_ptype(P): TYPE = {ps: prewalk | EXISTS (i: below(length(ps))): P(seq(ps)(i))}
first(P: pred[T],ps: ps_ptype(P)): below(length(ps)) =
min({i: nat | i < length(ps) AND P(seq(ps)(i))})
first_lem: LEMMA FORALL (ps: ps_ptype(P)): P(seq(ps)(first(P,ps)))
first_not: LEMMA FORALL (ps: ps_ptype(P)): i < first(P,ps) IMPLIES
NOT P(seq(ps)(i))
z: VAR T
meng_to_G_sep: LEMMA walk_from?(G, p, s, t) AND
in?(G, s, t, w1, w2) AND disjoint?(s, t, w1, w2) AND
separates(meng(G, s, t, w1, w2), singleton(z), s, t) AND
separable?(G, s, t) AND
separates(G, dbl(w1, w2), s, t) AND
NOT verts_of(p)(z)
IMPLIES sep_num(G, s, t) <= 1
prep_14: LEMMA vert(G)(s) AND vert(G)(t) AND
vert(G)(w1) AND vert(G)(w2) AND
disjoint?(s, t, w1, w2) AND
sep_num(meng(G, s, t, w1, w2),s,t) <= 1 AND
separates(meng(G, s, t, w1, w2), dbl(w1, w2), s, t) AND
separable?(G, s, t) AND
separates(G, dbl(w1, w2), s, t) AND
sep_num(G, s, t) = 2
IMPLIES sep_num(G,s,t) <= 1
line14: LEMMA separable?(G, s, t) AND
in?(G, s, t, w1, w2) AND
sep_num(G, s, t) = 2 AND
separates(G, dbl(w1, w2), s, t) AND
disjoint?(s, t, w1, w2)
IMPLIES
sep_num(meng(G, s, t, w1, w2), s, t) = 2
line15ab: LEMMA separable?(G,s,t) AND in?(G,s,t,w1,w2)
AND sep_num(G,s,t) = 2
AND separates(G, dbl(w1, w2), s, t)
IMPLIES
((EXISTS (Psw1: prewalk): path_from?(G,Psw1,s,w1)) AND
(EXISTS (Psw2: prewalk): path_from?(G,Psw2,s,w2)))
prep_16: LEMMA separates(G, dbl(w1, w2), s, t) AND
disjoint?(s, t, w1, w2) AND
(FORALL p: path_from?(G,p,t,w1) IMPLIES verts_of(p)(w2))
AND vert(G)(s) AND vert(G)(t)
IMPLIES sep_num(G,s,t) <= 1
line16: LEMMA NOT edge?(G)(w1, t) AND
disjoint?(s,t,w1,w2) AND
separates(G, dbl(w1, w2), s, t) AND
sep_num(G,s,t) = 2 AND vert(G)(s) AND vert(G)(t)
IMPLIES EXISTS (yt: T): vert(H(G,t,w1,w2))(yt) AND yt /= t
line19: LEMMA separable?(G,s,t) AND in?(G,s,t,w1,w2)
AND disjoint?(s,t,w1,w2)
AND MM = meng(G, s, t, w1, w2)
AND separates(G, dbl(w1, w2), s, t)
AND path_from?(MM, p, s, t)
IMPLIES length(p) > 2 AND ( seq(p)(length(p)-2) = w1
OR seq(p)(length(p)-2) = w2)
yt: VAR T
line17_prep: LEMMA vert(G)(s) AND vert(G)(t) AND disjoint?(s,t,w1,w2) AND
vert(H(G, t, w1, w2))(yt) AND
separates(G, dbl(w1, w2), s, t) IMPLIES
NOT vert(H(G, s, w1, w2))(yt)
line17: LEMMA vert(H(G,t,w1,w2))(yt) AND
in?(G, s, t, w1, w2) AND
disjoint?(s, t, w1, w2) AND
yt /= t AND
separates(G, dbl(w1, w2), s, t)
IMPLIES size(meng(G, s, t, w1, w2)) < size(G)
pre20: LEMMA separable?(G, s, t) AND
in?(G, s, t, w1, w2) AND
sep_num(G, s, t) = 2 AND
separates(G, dbl(w1, w2), s, t) AND
disjoint?(s, t, w1, w2)
IMPLIES
( separable?(meng(G, s, t, w1, w2),s,t) AND
sep_num(meng(G, s, t, w1, w2), s, t) = 2 AND
vert(meng(G, s, t, w1, w2))(s) AND
vert(meng(G, s, t, w1, w2))(t) )
END meng_scaff
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