let X be OrtAfPl; :: thesis: ( X is satisfying_OSCH & X is satisfying_TDES implies X is satisfying_SCH )
assume that
A1:
X is satisfying_OSCH
and
A2:
X is satisfying_TDES
; :: thesis: X is satisfying_SCH
let a1 be Element of X; :: according to CONMETR:def 6 :: thesis: for a2, a3, a4, b1, b2, b3, b4 being Element of X
for M, N being Subset of X st M is being_line & N is being_line & a1 in M & a3 in M & b1 in M & b3 in M & a2 in N & a4 in N & b2 in N & b4 in N & not a4 in M & not a2 in M & not b2 in M & not b4 in M & not a1 in N & not a3 in N & not b1 in N & not b3 in N & a3,a2 // b3,b2 & a2,a1 // b2,b1 & a1,a4 // b1,b4 holds
a3,a4 // b3,b4
let a2, a3, a4, b1, b2, b3, b4 be Element of X; :: thesis: for M, N being Subset of X st M is being_line & N is being_line & a1 in M & a3 in M & b1 in M & b3 in M & a2 in N & a4 in N & b2 in N & b4 in N & not a4 in M & not a2 in M & not b2 in M & not b4 in M & not a1 in N & not a3 in N & not b1 in N & not b3 in N & a3,a2 // b3,b2 & a2,a1 // b2,b1 & a1,a4 // b1,b4 holds
a3,a4 // b3,b4
let M, N be Subset of X; :: thesis: ( M is being_line & N is being_line & a1 in M & a3 in M & b1 in M & b3 in M & a2 in N & a4 in N & b2 in N & b4 in N & not a4 in M & not a2 in M & not b2 in M & not b4 in M & not a1 in N & not a3 in N & not b1 in N & not b3 in N & a3,a2 // b3,b2 & a2,a1 // b2,b1 & a1,a4 // b1,b4 implies a3,a4 // b3,b4 )
assume that
A3:
( M is being_line & N is being_line )
and
A4:
( a1 in M & a3 in M & b1 in M & b3 in M & a2 in N & a4 in N & b2 in N & b4 in N & not a4 in M & not a2 in M & not b2 in M & not b4 in M & not a1 in N & not a3 in N & not b1 in N & not b3 in N & a3,a2 // b3,b2 & a2,a1 // b2,b1 & a1,a4 // b1,b4 )
; :: thesis: a3,a4 // b3,b4
reconsider a1' = a1, a2' = a2, a3' = a3, a4' = a4, b1' = b1, b2' = b2, b3' = b3, b4' = b4 as Element of (Af X) by ANALMETR:47;
reconsider M' = M, N' = N as Subset of (Af X) by ANALMETR:57;
A5:
( M' is being_line & N' is being_line )
by A3, ANALMETR:58;
A6:
( a1 = b1 implies ( a2 = b2 & a3 = b3 & a4 = b4 ) )
proof
assume A7:
a1 = b1
;
:: thesis: ( a2 = b2 & a3 = b3 & a4 = b4 )
assume A8:
(
a2 <> b2 or
a3 <> b3 or
a4 <> b4 )
;
:: thesis: contradiction
A9:
now assume A10:
a2 <> b2
;
:: thesis: contradiction
a1,
a2 // a1,
b2
by A4, A7, ANALMETR:81;
then
LIN a1,
a2,
b2
by ANALMETR:def 11;
then
LIN a1',
a2',
b2'
by ANALMETR:55;
then
LIN a2',
b2',
a1'
by AFF_1:15;
hence
contradiction
by A4, A5, A10, AFF_1:39;
:: thesis: verum end;
A11:
now assume A12:
a4 <> b4
;
:: thesis: contradiction
LIN a1,
a4,
b4
by A4, A7, ANALMETR:def 11;
then
LIN a1',
a4',
b4'
by ANALMETR:55;
then
LIN a4',
b4',
a1'
by AFF_1:15;
hence
contradiction
by A4, A5, A12, AFF_1:39;
:: thesis: verum end;
now assume A13:
a3 <> b3
;
:: thesis: contradiction
a2,
a3 // a2,
b3
by A4, A9, ANALMETR:81;
then
LIN a2,
a3,
b3
by ANALMETR:def 11;
then
LIN a2',
a3',
b3'
by ANALMETR:55;
then
LIN a3',
b3',
a2'
by AFF_1:15;
hence
contradiction
by A4, A5, A13, AFF_1:39;
:: thesis: verum end;
hence
contradiction
by A8, A9, A11;
:: thesis: verum
end;
A15:
( a1 <> b1 implies ( a2 <> b2 & a3 <> b3 & a4 <> b4 ) )
proof
assume A16:
a1 <> b1
;
:: thesis: ( a2 <> b2 & a3 <> b3 & a4 <> b4 )
assume A17:
(
a2 = b2 or
a3 = b3 or
a4 = b4 )
;
:: thesis: contradiction
A18:
now assume
a2 = b2
;
:: thesis: contradictionthen
LIN a2,
a1,
b1
by A4, ANALMETR:def 11;
then
LIN a2',
a1',
b1'
by ANALMETR:55;
then
LIN a1',
b1',
a2'
by AFF_1:15;
hence
contradiction
by A4, A5, A16, AFF_1:39;
:: thesis: verum end;
A19:
now assume
a4 = b4
;
:: thesis: contradictionthen
a4,
a1 // a4,
b1
by A4, ANALMETR:81;
then
LIN a4,
a1,
b1
by ANALMETR:def 11;
then
LIN a4',
a1',
b1'
by ANALMETR:55;
then
LIN a1',
b1',
a4'
by AFF_1:15;
hence
contradiction
by A4, A5, A16, AFF_1:39;
:: thesis: verum end;
now assume
a3 = b3
;
:: thesis: contradictionthen
LIN a3,
a2,
b2
by A4, ANALMETR:def 11;
then
LIN a3',
a2',
b2'
by ANALMETR:55;
then
LIN a2',
b2',
a3'
by AFF_1:15;
hence
contradiction
by A4, A5, A18, AFF_1:39;
:: thesis: verum end;
hence
contradiction
by A17, A18, A19;
:: thesis: verum
end;
now assume A20:
a1 <> b1
;
:: thesis: a3,a4 // b3,b4A21:
now assume A22:
a2 = a4
;
:: thesis: a3,a4 // b3,b4A23:
not
LIN a2',
b1',
b2'
A24:
LIN a2',
b2',
b4'
b1',
b2' // b1',
b4'
proof
a2,
a1 // b1,
b4
by A4, A22, ANALMETR:81;
then
b2,
b1 // b1,
b4
by A4, ANALMETR:82;
then
b1,
b2 // b1,
b4
by ANALMETR:81;
hence
b1',
b2' // b1',
b4'
by ANALMETR:48;
:: thesis: verum
end; hence
a3,
a4 // b3,
b4
by A4, A22, A23, A24, AFF_1:23;
:: thesis: verum end; A25:
now assume A26:
a1 = a3
;
:: thesis: a3,a4 // b3,b4A27:
not
LIN a1',
b2',
b1'
A28:
LIN a1',
b1',
b3'
b2',
b1' // b2',
b3'
hence
a3,
a4 // b3,
b4
by A4, A26, A27, A28, AFF_1:23;
:: thesis: verum end; now assume A29:
(
a2 <> a4 &
a1 <> a3 )
;
:: thesis: a3,a4 // b3,b4A30:
now assume A31:
M // N
;
:: thesis: a3,a4 // b3,b4consider x being
Element of
X such that A32:
(
LIN a1,
a2,
x &
a1 <> x &
a2 <> x )
by A4, Th2;
reconsider x' =
x as
Element of
(Af X) by ANALMETR:47;
consider e1 being
Element of
X such that A33:
(
b1,
b2 // b1,
e1 &
b1 <> e1 )
by ANALMETR:51;
consider e2 being
Element of
X such that A34:
(
a1,
b1 // x,
e2 &
x <> e2 )
by ANALMETR:51;
reconsider e1' =
e1,
e2' =
e2 as
Element of
(Af X) by ANALMETR:47;
not
b1',
e1' // x',
e2'
proof
assume
b1',
e1' // x',
e2'
;
:: thesis: contradiction
then
b1,
e1 // x,
e2
by ANALMETR:48;
then
b1,
b2 // x,
e2
by A33, ANALMETR:82;
then
b1,
b2 // a1,
b1
by A34, ANALMETR:82;
then
b1,
a1 // b1,
b2
by ANALMETR:81;
then
LIN b1,
a1,
b2
by ANALMETR:def 11;
then
LIN b1',
a1',
b2'
by ANALMETR:55;
hence
contradiction
by A4, A5, A20, AFF_1:39;
:: thesis: verum
end; then consider y' being
Element of
(Af X) such that A35:
(
LIN b1',
e1',
y' &
LIN x',
e2',
y' )
by AFF_1:74;
reconsider y =
y' as
Element of
X by ANALMETR:47;
A36:
LIN b1,
b2,
y
proof
LIN b1,
e1,
y
by A35, ANALMETR:55;
then
b1,
e1 // b1,
y
by ANALMETR:def 11;
then
b1,
b2 // b1,
y
by A33, ANALMETR:82;
hence
LIN b1,
b2,
y
by ANALMETR:def 11;
:: thesis: verum
end; A37:
a1,
b1 // x,
y
A38:
(
X is
satisfying_TDES implies
X is
satisfying_des )
A39:
not
LIN a1,
b1,
x
proof
assume
LIN a1,
b1,
x
;
:: thesis: contradiction
then
LIN a1',
b1',
x'
by ANALMETR:55;
then A40:
x' in M'
by A4, A5, A20, AFF_1:39;
LIN a1',
a2',
x'
by A32, ANALMETR:55;
then
LIN a1',
x',
a2'
by AFF_1:15;
hence
contradiction
by A4, A5, A32, A40, AFF_1:39;
:: thesis: verum
end; A41:
not
LIN a1,
b1,
a4
A42:
a1,
b1 // a4,
b4
A43:
a1,
x // b1,
y
proof
A44:
b1,
b2 // b1,
y
by A36, ANALMETR:def 11;
a1,
a2 // b1,
b2
by A4, ANALMETR:81;
then A45:
a1,
a2 // b1,
y
by A4, A44, ANALMETR:82;
a1,
a2 // a1,
x
by A32, ANALMETR:def 11;
hence
a1,
x // b1,
y
by A4, A45, ANALMETR:82;
:: thesis: verum
end; then A46:
x,
a4 // y,
b4
by A2, A4, A37, A38, A39, A41, A42, Def8;
A47:
not
LIN a2,
b2,
x
proof
assume
LIN a2,
b2,
x
;
:: thesis: contradiction
then A48:
LIN a2',
b2',
x'
by ANALMETR:55;
a2 <> b2
proof
assume
a2 = b2
;
:: thesis: contradiction
then
LIN a2,
a1,
b1
by A4, ANALMETR:def 11;
then
LIN a2',
a1',
b1'
by ANALMETR:55;
then
LIN a1',
b1',
a2'
by AFF_1:15;
hence
contradiction
by A4, A5, A20, AFF_1:39;
:: thesis: verum
end;
then A49:
x' in N'
by A4, A5, A48, AFF_1:39;
LIN a1',
a2',
x'
by A32, ANALMETR:55;
then
LIN a2',
x',
a1'
by AFF_1:15;
hence
contradiction
by A4, A5, A32, A49, AFF_1:39;
:: thesis: verum
end; A50:
not
LIN a2,
b2,
a3
proof
assume
LIN a2,
b2,
a3
;
:: thesis: contradiction
then A51:
LIN a2',
b2',
a3'
by ANALMETR:55;
a2 <> b2
proof
assume
a2 = b2
;
:: thesis: contradiction
then
LIN a2,
a1,
b1
by A4, ANALMETR:def 11;
then
LIN a2',
a1',
b1'
by ANALMETR:55;
then
LIN a1',
b1',
a2'
by AFF_1:15;
hence
contradiction
by A4, A5, A20, AFF_1:39;
:: thesis: verum
end;
hence
contradiction
by A4, A5, A51, AFF_1:39;
:: thesis: verum
end; A52:
a2,
b2 // x,
y
proof
M' // N'
by A31, ANALMETR:64;
then
a1',
b1' // a2',
b2'
by A4, AFF_1:53;
then
a1,
b1 // a2,
b2
by ANALMETR:48;
hence
a2,
b2 // x,
y
by A20, A37, ANALMETR:82;
:: thesis: verum
end; A53:
a2,
b2 // a3,
b3
A54:
a2,
x // b2,
y
proof
LIN a1',
a2',
x'
by A32, ANALMETR:55;
then
LIN x',
a1',
a2'
by AFF_1:15;
then
LIN x,
a1,
a2
by ANALMETR:55;
then
x,
a1 // x,
a2
by ANALMETR:def 11;
then
a1,
x // a2,
x
by ANALMETR:81;
then A55:
a2,
x // b1,
y
by A32, A43, ANALMETR:82;
A56:
b1 <> y
proof
assume
b1 = y
;
:: thesis: contradiction
then
b1,
a1 // b1,
x
by A37, ANALMETR:81;
then
LIN b1,
a1,
x
by ANALMETR:def 11;
then
LIN b1',
a1',
x'
by ANALMETR:55;
then A57:
x' in M'
by A4, A5, A20, AFF_1:39;
LIN a1',
a2',
x'
by A32, ANALMETR:55;
then
LIN a1',
x',
a2'
by AFF_1:15;
hence
contradiction
by A4, A5, A32, A57, AFF_1:39;
:: thesis: verum
end;
LIN b1',
b2',
y'
by A36, ANALMETR:55;
then
LIN y',
b1',
b2'
by AFF_1:15;
then
LIN y,
b1,
b2
by ANALMETR:55;
then
y,
b1 // y,
b2
by ANALMETR:def 11;
then
b1,
y // b2,
y
by ANALMETR:81;
hence
a2,
x // b2,
y
by A55, A56, ANALMETR:82;
:: thesis: verum
end;
a2,
a3 // b2,
b3
by A4, ANALMETR:81;
then A58:
x,
a3 // y,
b3
by A2, A38, A47, A50, A52, A53, A54, Def8;
A59:
not
LIN x,
y,
a3
proof
assume
LIN x,
y,
a3
;
:: thesis: contradiction
then A60:
x,
y // x,
a3
by ANALMETR:def 11;
A61:
x <> y
proof
assume
x = y
;
:: thesis: contradiction
then
x,
a1 // x,
b1
by A43, ANALMETR:81;
then
LIN x,
a1,
b1
by ANALMETR:def 11;
then
LIN x',
a1',
b1'
by ANALMETR:55;
then
LIN a1',
b1',
x'
by AFF_1:15;
then A62:
x' in M'
by A4, A5, A20, AFF_1:39;
LIN a1',
a2',
x'
by A32, ANALMETR:55;
then
LIN x',
a1',
a2'
by AFF_1:15;
hence
contradiction
by A4, A5, A32, A62, AFF_1:39;
:: thesis: verum
end;
M' // M'
by A5, AFF_1:55;
then
a1',
a3' // a1',
b1'
by A4, AFF_1:53;
then
a1,
a3 // a1,
b1
by ANALMETR:48;
then
x,
y // a1,
a3
by A20, A37, ANALMETR:82;
then
x,
a3 // a1,
a3
by A60, A61, ANALMETR:82;
then
a3,
a1 // a3,
x
by ANALMETR:81;
then
LIN a3,
a1,
x
by ANALMETR:def 11;
then
LIN a3',
a1',
x'
by ANALMETR:55;
then A63:
x' in M'
by A4, A5, A29, AFF_1:39;
LIN a1',
a2',
x'
by A32, ANALMETR:55;
then
LIN a1',
x',
a2'
by AFF_1:15;
hence
contradiction
by A4, A5, A32, A63, AFF_1:39;
:: thesis: verum
end; A64:
not
LIN x,
y,
a4
proof
assume
LIN x,
y,
a4
;
:: thesis: contradiction
then A65:
x,
y // x,
a4
by ANALMETR:def 11;
A66:
x <> y
proof
assume
x = y
;
:: thesis: contradiction
then
x,
a1 // x,
b1
by A43, ANALMETR:81;
then
LIN x,
a1,
b1
by ANALMETR:def 11;
then
LIN x',
a1',
b1'
by ANALMETR:55;
then
LIN a1',
b1',
x'
by AFF_1:15;
then A67:
x' in M'
by A4, A5, A20, AFF_1:39;
LIN a1',
a2',
x'
by A32, ANALMETR:55;
then
LIN x',
a1',
a2'
by AFF_1:15;
hence
contradiction
by A4, A5, A32, A67, AFF_1:39;
:: thesis: verum
end;
M' // N'
by A31, ANALMETR:64;
then
a1',
b1' // a2',
a4'
by A4, AFF_1:53;
then
a1,
b1 // a2,
a4
by ANALMETR:48;
then
a2,
a4 // x,
y
by A20, A37, ANALMETR:82;
then
a2,
a4 // x,
a4
by A65, A66, ANALMETR:82;
then
a4,
a2 // a4,
x
by ANALMETR:81;
then
LIN a4,
a2,
x
by ANALMETR:def 11;
then
LIN a4',
a2',
x'
by ANALMETR:55;
then A68:
x' in N'
by A4, A5, A29, AFF_1:39;
LIN a1',
a2',
x'
by A32, ANALMETR:55;
then
LIN a2',
x',
a1'
by AFF_1:15;
hence
contradiction
by A4, A5, A32, A68, AFF_1:39;
:: thesis: verum
end; A69:
x,
y // a3,
b3
proof
M' // M'
by A5, AFF_1:55;
then
a1',
b1' // a3',
b3'
by A4, AFF_1:53;
then
a1,
b1 // a3,
b3
by ANALMETR:48;
hence
x,
y // a3,
b3
by A20, A37, ANALMETR:82;
:: thesis: verum
end;
x,
y // a4,
b4
proof
M' // N'
by A31, ANALMETR:64;
then
a1',
b1' // a4',
b4'
by A4, AFF_1:53;
then
a1,
b1 // a4,
b4
by ANALMETR:48;
hence
x,
y // a4,
b4
by A20, A37, ANALMETR:82;
:: thesis: verum
end; hence
a3,
a4 // b3,
b4
by A2, A38, A46, A58, A59, A64, A69, Def8;
:: thesis: verum end; now assume
not
M // N
;
:: thesis: a3,a4 // b3,b4then
not
M' // N'
by ANALMETR:64;
then consider o' being
Element of
(Af X) such that A70:
(
o' in M' &
o' in N' )
by A5, AFF_1:72;
reconsider o =
o' as
Element of
X by ANALMETR:47;
consider K being
Subset of
X such that A71:
(
o in K &
N _|_ K )
by A3, Th3;
reconsider K' =
K as
Subset of
(Af X) by ANALMETR:57;
A72:
K is
being_line
by A71, ANALMETR:62;
then A73:
(
K' is
being_line &
N' is
being_line )
by A3, ANALMETR:58;
now assume A74:
K <> M
;
:: thesis: a3,a4 // b3,b4then consider d1' being
Element of
(Af X) such that A78:
(
d1' in K' &
a1',
d1' // N' )
;
consider d3' being
Element of
(Af X) such that A79:
(
d3' in K' &
a3',
d3' // N' )
by A75;
consider e3' being
Element of
(Af X) such that A80:
(
e3' in K' &
b3',
e3' // N' )
by A75;
consider e1' being
Element of
(Af X) such that A81:
(
e1' in K' &
b1',
e1' // N' )
by A75;
reconsider d1 =
d1',
d3 =
d3',
e1 =
e1',
e3 =
e3' as
Element of
X by ANALMETR:47;
A82:
(
o <> e1 &
o <> e3 &
o <> d1 &
o <> d3 )
proof
assume A83:
( not
o <> e1 or not
o <> e3 or not
o <> d1 or not
o <> d3 )
;
:: thesis: contradiction
now let x,
y be
Element of
X;
:: thesis: for x', y' being Element of the carrier of (Af X) st x',y' // N' & x = x' & y = y' & x in M & y in K & not x in N holds
not o = ylet x',
y' be
Element of the
carrier of
(Af X);
:: thesis: ( x',y' // N' & x = x' & y = y' & x in M & y in K & not x in N implies not o = y )assume that A84:
x',
y' // N'
and A85:
(
x = x' &
y = y' )
and A86:
(
x in M &
y in K & not
x in N )
;
:: thesis: not o = yassume
o = y
;
:: thesis: contradictionthen
o',
x' // N'
by A84, A85, AFF_1:48;
hence
contradiction
by A5, A70, A85, A86, AFF_1:37;
:: thesis: verum end;
hence
contradiction
by A4, A78, A79, A80, A81, A83;
:: thesis: verum
end; A87:
(
LIN o,
a2,
b2 &
LIN o,
a1,
b1 &
LIN o,
a4,
b4 &
LIN o,
a3,
b3 )
by A3, A4, A70, Th4;
A88:
(
LIN o,
d1,
e1 &
LIN o,
d3,
e3 )
by A71, A72, A78, A79, A80, A81, Th4;
A89:
( not
LIN a1,
b1,
d1 & not
LIN a1,
b1,
a2 & not
LIN a1,
b1,
a4 & not
LIN a3,
b3,
d3 & not
LIN a3,
b3,
a2 )
proof
A90:
now assume
LIN a1,
b1,
d1
;
:: thesis: contradictionthen
LIN a1',
b1',
d1'
by ANALMETR:55;
then
d1 in M
by A4, A5, A20, AFF_1:39;
hence
contradiction
by A3, A70, A71, A72, A74, A78, A82, Th5;
:: thesis: verum end;
A93:
now assume
LIN a3,
b3,
d3
;
:: thesis: contradictionthen
LIN a3',
b3',
d3'
by ANALMETR:55;
then
d3 in M
by A4, A5, A15, A20, AFF_1:39;
hence
contradiction
by A3, A70, A71, A72, A74, A79, A82, Th5;
:: thesis: verum end;
hence
( not
LIN a1,
b1,
d1 & not
LIN a1,
b1,
a2 & not
LIN a1,
b1,
a4 & not
LIN a3,
b3,
d3 & not
LIN a3,
b3,
a2 )
by A90, A91, A92, A93;
:: thesis: verum
end; A94:
d1,
a1 // e1,
b1
A95:
d1,
a1 // o,
a2
a1,
a2 // b1,
b2
by A4, ANALMETR:81;
then
d1,
a2 // e1,
b2
by A2, A4, A70, A82, A87, A88, A89, A94, A95, Def5;
then A96:
a2,
d1 // b2,
e1
by ANALMETR:81;
d1,
a1 // o,
a4
then A97:
d1,
a4 // e1,
b4
by A2, A4, A70, A82, A87, A88, A89, A94, Def5;
A98:
d3,
a3 // e3,
b3
d3,
a3 // o,
a2
then A99:
d3,
a2 // e3,
b2
by A2, A4, A70, A82, A87, A88, A89, A98, Def5;
A100:
( not
d1 in N & not
d3 in N & not
e1 in N & not
e3 in N )
by A4, A78, A79, A80, A81, AFF_1:49;
( not
a2 in K & not
a4 in K & not
b2 in K & not
b4 in K )
then A103:
d3,
a4 // e3,
b4
by A1, A4, A71, A78, A79, A80, A81, A96, A97, A99, A100, Def7;
A104:
( not
LIN d3,
e3,
a3 & not
LIN d3,
e3,
a4 )
proof
A105:
d3 <> e3
proof
assume
not
d3 <> e3
;
:: thesis: contradiction
then
LIN e3,
a3,
b3
by A98, ANALMETR:def 11;
then
LIN e3',
a3',
b3'
by ANALMETR:55;
then
LIN a3',
b3',
e3'
by AFF_1:15;
then
e3' in M'
by A4, A5, A15, A20, AFF_1:39;
hence
contradiction
by A5, A70, A71, A73, A74, A80, A82, AFF_1:30;
:: thesis: verum
end;
assume
(
LIN d3,
e3,
a3 or
LIN d3,
e3,
a4 )
;
:: thesis: contradiction
then
(
LIN d3',
e3',
a3' or
LIN d3',
e3',
a4' )
by ANALMETR:55;
then
(
a3' in K' or
a4' in K' )
by A73, A79, A80, A105, AFF_1:39;
hence
contradiction
by A4, A5, A70, A71, A73, A74, AFF_1:30;
:: thesis: verum
end; A106:
a3,
d3 // b3,
e3
by A98, ANALMETR:81;
a3,
d3 // o,
a4
by A4, A70, A79, Th6;
hence
a3,
a4 // b3,
b4
by A2, A4, A70, A82, A87, A88, A103, A104, A106, Def5;
:: thesis: verum end; hence
a3,
a4 // b3,
b4
by A1, A4, A71, Def7;
:: thesis: verum end; hence
a3,
a4 // b3,
b4
by A30;
:: thesis: verum end; hence
a3,
a4 // b3,
b4
by A21, A25;
:: thesis: verum end;
hence
a3,a4 // b3,b4
by A14; :: thesis: verum