graph_conn_piece[T: TYPE]: THEORY
BEGIN
IMPORTING graph_conn_defs[T]
G,H1,H2: VAR graph[T]
x,y,v: VAR T
% piece_connected?(G): bool = NOT empty?(G) AND
% (FORALL H1,H2: G = union(H1,H2) AND
% NOT empty?(H1) AND NOT empty?(H2)
% IMPLIES NOT empty?(intersection(vert(H1),
% vert(H2))))
singleton_piece: LEMMA singleton?(G) IMPLIES
piece_connected?(G)
not_piece_has_2: LEMMA NOT piece_connected?(G) IMPLIES empty?(G) OR
size(G) > 1
e: VAR doubleton[T]
vo: VAR T
edge_not_across: LEMMA e(vo) AND vert(H1)(vo) AND
edges(union(H1, H2))(e) AND
empty?(intersection(vert(H1), vert(H2)))
IMPLIES edges(H1)(e)
lem1: LEMMA vert(H1)(vo) AND empty?(intersection(vert(H1), vert(H2))) AND
NOT empty?(H1) AND NOT empty?(H2)
IMPLIES del_vert(union(H1, H2), vo) = union(del_vert(H1, vo), H2)
H1P_not_empty: LEMMA vert(H1)(vo) AND
deg(vo, union(H1, H2)) > 0 AND
del_vert(G, vo) = union(del_vert(H1, vo), H2) AND
empty?(intersection(vert(H1), vert(H2))) AND
NOT empty?(H1) AND NOT empty?(H2) AND
NOT empty?(del_vert(G, vo))
IMPLIES NOT empty?(del_vert(H1, vo))
cip0: LEMMA (FORALL (GG: graph[T]): size(GG) < size(G)
IMPLIES connected?(GG) IMPLIES piece_connected?(GG)) AND
vert(H1)(vo) AND
deg(vo, G) > 0 AND
connected?(del_vert(G, vo)) AND
G = union(H1, H2) AND
empty?(intersection(vert(H1), vert(H2))) AND
NOT empty?(H1) AND NOT empty?(H2)
IMPLIES NOT empty?(intersection(vert(H1), vert(H2)))
cip3: LEMMA (FORALL (GG: graph[T]): size(GG) < size(G)
IMPLIES connected?(GG) IMPLIES piece_connected?(GG)) AND
deg(vo, G) > 0 AND
connected?(del_vert(G, vo)) AND
G = union(H1, H2) AND
NOT empty?(H1) AND NOT empty?(H2) AND vert(G)(vo)
IMPLIES NOT empty?(intersection(vert(H1), vert(H2)))
connected_not_empty: LEMMA connected?(G) IMPLIES NOT empty?(G)
IMPORTING graph_inductions[T]
conn_implies_piece: LEMMA connected?(G) IMPLIES piece_connected?(G)
END graph_conn_piece
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