:: Characterization and Existence of {G}r\"obner Bases
:: by Christoph Schwarzweller
::
:: Received June 11, 2003
:: Copyright (c) 2003-2017 Association of Mizar Users
:: (Stowarzyszenie Uzytkownikow Mizara, Bialystok, Poland).
:: This code can be distributed under the GNU General Public Licence
:: version 3.0 or later, or the Creative Commons Attribution-ShareAlike
:: License version 3.0 or later, subject to the binding interpretation
:: detailed in file COPYING.interpretation.
:: See COPYING.GPL and COPYING.CC-BY-SA for the full text of these
:: licenses, or see http://www.gnu.org/licenses/gpl.html and
:: http://creativecommons.org/licenses/by-sa/3.0/.
environ
vocabularies NUMBERS, ORDINAL1, RLVECT_1, ALGSTR_0, VECTSP_1, LATTICES,
ZFMISC_1, POLYNOM1, SUBSET_1, STRUCT_0, RELAT_2, BAGORDER, BINOP_1,
POLYRED, POLYNOM7, ARYTM_1, ARYTM_3, PRE_POLY, TERMORD, FUNCT_1, BROUWER,
RELAT_1, XBOOLE_0, XXREAL_0, SUPINF_2, VALUED_0, XCMPLX_0, CAT_3,
ALGSTR_1, IDEAL_1, FINSEQ_1, PARTFUN1, MESFUNC1, CARD_3, TARSKI, CARD_1,
ORDERS_2, REWRITE1, INT_1, FUNCT_4, GROUP_1, ORDERS_1, DICKSON, RLVECT_2,
FUNCOP_1, PBOOLE, FINSET_1, ORDINAL4, GROEB_1, NAT_1;
notations TARSKI, RELAT_1, XBOOLE_0, RELAT_2, XCMPLX_0, XXREAL_0, RELSET_1,
FUNCT_1, PARTFUN1, ORDINAL1, ALGSTR_0, ALGSTR_1, RLVECT_1, FINSET_1,
FUNCT_7, DICKSON, CARD_3, CARD_1, SUBSET_1, XTUPLE_0, MCART_1, FINSEQ_1,
YELLOW_1, ORDERS_1, PRALG_1, STRUCT_0, POLYNOM7, PBOOLE, FUNCOP_1,
ORDERS_2, VFUNCT_1, POLYNOM1, IDEAL_1, REWRITE1, BAGORDER, VECTSP_1,
TERMORD, GROUP_1, NUMBERS, NAT_1, PRE_POLY, POLYRED, RECDEF_1;
constructors REWRITE1, VECTSP_2, PRALG_1, YELLOW_1, IDEAL_1, DICKSON,
BAGORDER, TERMORD, POLYRED, RECDEF_1, DOMAIN_1, RELSET_1, PBOOLE,
FUNCT_7, VFUNCT_1, XTUPLE_0;
registrations XBOOLE_0, RELAT_1, ORDINAL1, FINSET_1, XREAL_0, NAT_1, INT_1,
CARD_1, REWRITE1, STRUCT_0, VECTSP_1, ORDERS_2, ALGSTR_1, YELLOW_1,
GCD_1, POLYNOM1, POLYNOM2, POLYNOM4, IDEAL_1, POLYNOM7, DICKSON, TERMORD,
POLYRED, VALUED_0, ALGSTR_0, FINSEQ_1, SUBSET_1, PRE_POLY, FUNCOP_1,
VFUNCT_1, FUNCT_1, FUNCT_2;
requirements NUMERALS, REAL, SUBSET, BOOLE, ARITHM;
begin :: Preliminaries
definition
let n be Ordinal, L be right_zeroed add-associative right_complementable
well-unital distributive non trivial doubleLoopStr, p be Polynomial of n,L;
redefine func {p} -> Subset of Polynom-Ring(n,L);
end;
theorem :: GROEB_1:1
for n being Ordinal, T being connected TermOrder of n, L being
add-associative right_complementable right_zeroed commutative associative
well-unital distributive almost_left_invertible non trivial doubleLoopStr, f,
p,g being Polynomial of n,L holds f reduces_to g,p,T implies ex m being
Monomial of n,L st g = f - m *' p;
theorem :: GROEB_1:2
for n being Ordinal, T being admissible connected TermOrder of n, L
being add-associative right_complementable right_zeroed commutative associative
well-unital distributive Abelian almost_left_invertible non degenerated non
empty doubleLoopStr, f,p,g being Polynomial of n,L holds f reduces_to g,p,T
implies ex m being Monomial of n,L st g = f - m *' p & not(HT(m*'p,T) in
Support g) & HT(m*'p,T) <= HT(f,T),T;
theorem :: GROEB_1:3
for n being Ordinal, T being connected TermOrder of n, L being
add-associative right_complementable right_zeroed commutative associative
well-unital distributive almost_left_invertible non trivial doubleLoopStr, f,
g being Polynomial of n,L, P,Q being Subset of Polynom-Ring(n,L) st P c= Q
holds f reduces_to g,P,T implies f reduces_to g,Q,T;
theorem :: GROEB_1:4
for n being Ordinal, T being connected TermOrder of n, L being
add-associative right_complementable right_zeroed commutative associative
well-unital distributive almost_left_invertible non trivial doubleLoopStr, P,
Q being Subset of Polynom-Ring(n,L) holds P c= Q implies PolyRedRel(P,T) c=
PolyRedRel(Q,T);
theorem :: GROEB_1:5
for n being Ordinal, L being right_zeroed add-associative
right_complementable non empty doubleLoopStr, p being Polynomial of n,L holds
Support(-p) = Support(p);
theorem :: GROEB_1:6
for n being Ordinal, T being connected TermOrder of n, L being
right_zeroed add-associative right_complementable well-unital distributive non
trivial non empty doubleLoopStr, p being Polynomial of n,L holds HT(-p,T) =
HT(p,T);
theorem :: GROEB_1:7
for n being Ordinal, T being admissible connected TermOrder of n,
L being right_zeroed add-associative right_complementable well-unital
distributive non trivial doubleLoopStr, p,q being Polynomial of n,L
holds HT(p-q,T) <= max(HT(p,T),HT(q,T),T), T;
theorem :: GROEB_1:8
for n being Ordinal, T being admissible connected TermOrder of n,
L being add-associative right_complementable right_zeroed commutative
associative well-unital distributive almost_left_invertible non trivial
doubleLoopStr, p,q being Polynomial of n,L holds Support(q) c= Support(p)
implies q <= p,T;
theorem :: GROEB_1:9
for n being Ordinal, T being connected admissible TermOrder of n,
L being add-associative right_complementable right_zeroed commutative
associative well-unital distributive almost_left_invertible non degenerated
non empty doubleLoopStr, f,p being non-zero Polynomial of n,L holds f
is_reducible_wrt p,T implies HT(p,T) <= HT(f,T),T;
begin :: Characterization of Groebner Bases
theorem :: GROEB_1:10
for n being Element of NAT, T being connected admissible
TermOrder of n, L being add-associative right_complementable right_zeroed
commutative associative well-unital distributive Abelian almost_left_invertible
non trivial doubleLoopStr, p being Polynomial of n,L holds PolyRedRel({p},T)
is locally-confluent;
theorem :: GROEB_1:11 :: corollary 5.34, p. 205
for n being Element of NAT, T being connected admissible TermOrder of
n, L being Abelian add-associative right_complementable right_zeroed
commutative associative well-unital distributive almost_left_invertible non
degenerated non empty doubleLoopStr, P being Subset of Polynom-Ring(n,L) st
ex p being Polynomial of n,L st p in P & P-Ideal = {p}-Ideal holds PolyRedRel(P
,T) is locally-confluent;
definition
let n be Ordinal, T be connected TermOrder of n, L be right_zeroed
add-associative right_complementable well-unital distributive non trivial non
empty doubleLoopStr, P be Subset of Polynom-Ring(n,L);
func HT(P,T) -> Subset of Bags n equals
:: GROEB_1:def 1
{ HT(p,T) where p is Polynomial of n
,L : p in P & p <> 0_(n,L) };
end;
definition
let n be Ordinal, S be Subset of Bags n;
func multiples(S) -> Subset of Bags n equals
:: GROEB_1:def 2
{ b where b is Element of Bags
n: ex b9 being bag of n st b9 in S & b9 divides b };
end;
theorem :: GROEB_1:12 :: theorem 5.35 (i) ==> (ii), p. 206
for n being Element of NAT, T being connected admissible TermOrder of
n, L being add-associative right_complementable right_zeroed commutative
associative well-unital distributive Abelian almost_left_invertible non
degenerated non empty doubleLoopStr, P being Subset of Polynom-Ring(n,L)
holds PolyRedRel(P,T) is locally-confluent implies PolyRedRel(P,T) is confluent
;
theorem :: GROEB_1:13 :: theorem 5.35 (ii) ==> (iii), p. 206
for n being Ordinal, T being connected TermOrder of n, L being
add-associative right_complementable right_zeroed commutative associative
well-unital distributive almost_left_invertible non trivial doubleLoopStr, P
being Subset of Polynom-Ring(n,L) holds PolyRedRel(P,T) is confluent implies
PolyRedRel(P,T) is with_UN_property;
theorem :: GROEB_1:14 :: theorem 5.35 (iii) ==> (iv), p. 206
for n being Element of NAT, T being connected admissible TermOrder of
n, L being add-associative right_complementable right_zeroed commutative
associative well-unital distributive Abelian almost_left_invertible non
degenerated non empty doubleLoopStr, P being Subset of Polynom-Ring(n,L)
holds PolyRedRel(P,T) is with_UN_property implies PolyRedRel(P,T) is
with_Church-Rosser_property;
theorem :: GROEB_1:15 :: theorem 5.35 (iv) ==> (v), p. 206
for n being Element of NAT, T being connected admissible
TermOrder of n, L being add-associative right_complementable right_zeroed
commutative associative well-unital distributive Abelian almost_left_invertible
non degenerated non empty doubleLoopStr, P being non empty Subset of
Polynom-Ring(n,L) holds PolyRedRel(P,T) is with_Church-Rosser_property implies
(for f being Polynomial of n,L st f in P-Ideal holds PolyRedRel(P,T) reduces f,
0_(n,L));
theorem :: GROEB_1:16 :: theorem 5.35 (v) ==> (vi), p. 206
for n being Ordinal, T being connected TermOrder of n, L being
add-associative right_complementable right_zeroed commutative associative
well-unital distributive almost_left_invertible non trivial doubleLoopStr, P
being Subset of Polynom-Ring(n,L) holds (for f being Polynomial of n,L st f in
P-Ideal holds PolyRedRel(P,T) reduces f,0_(n,L)) implies (for f being non-zero
Polynomial of n,L st f in P-Ideal holds f is_reducible_wrt P,T);
theorem :: GROEB_1:17 :: theorem 5.35 (vi) ==> (vii), p. 206
for n being Element of NAT, T being admissible connected
TermOrder of n, L being add-associative right_complementable right_zeroed
commutative associative well-unital distributive Abelian almost_left_invertible
non degenerated non empty doubleLoopStr, P being Subset of Polynom-Ring(n,L)
holds (for f being non-zero Polynomial of n,L st f in P-Ideal holds f
is_reducible_wrt P,T) implies (for f being non-zero Polynomial of n,L st f in P
-Ideal holds f is_top_reducible_wrt P,T);
theorem :: GROEB_1:18 :: theorem 5.35 (vii) ==> (viii), p. 206
for n being Ordinal, T being connected TermOrder of n, L being
add-associative right_complementable right_zeroed commutative associative
well-unital distributive almost_left_invertible non trivial doubleLoopStr, P
being Subset of Polynom-Ring(n,L) holds (for f being non-zero Polynomial of n,L
st f in P-Ideal holds f is_top_reducible_wrt P,T) implies (for b being bag of n
st b in HT(P-Ideal,T) ex b9 being bag of n st b9 in HT(P,T) & b9 divides b);
theorem :: GROEB_1:19 :: theorem 5.35 (viii) ==> (ix), p. 206
for n being Ordinal, T being connected TermOrder of n, L being
add-associative right_complementable right_zeroed commutative associative
well-unital distributive almost_left_invertible non trivial doubleLoopStr, P
being Subset of Polynom-Ring(n,L) holds (for b being bag of n st b in HT(P
-Ideal,T) ex b9 being bag of n st b9 in HT(P,T) & b9 divides b) implies HT(P
-Ideal,T) c= multiples(HT(P,T));
theorem :: GROEB_1:20 :: theorem 5.35 (ix) ==> (i), p. 206
for n being Element of NAT, T being connected admissible TermOrder of
n, L being Abelian add-associative right_complementable right_zeroed
commutative associative well-unital distributive almost_left_invertible non
degenerated non empty doubleLoopStr, P being Subset of Polynom-Ring(n,L)
holds HT(P-Ideal,T) c= multiples(HT(P,T)) implies PolyRedRel(P,T) is
locally-confluent;
definition :: definition 5.37, p. 207
let n be Ordinal, T be connected TermOrder of n, L be add-associative
right_complementable right_zeroed commutative associative well-unital
distributive almost_left_invertible non trivial doubleLoopStr, G be Subset of
Polynom-Ring(n,L);
pred G is_Groebner_basis_wrt T means
:: GROEB_1:def 3
PolyRedRel(G,T) is locally-confluent;
end;
definition :: definition 5.37, p. 207
let n be Ordinal, T be connected TermOrder of n, L be add-associative
right_complementable right_zeroed commutative associative well-unital
distributive almost_left_invertible non trivial doubleLoopStr, G,I be Subset
of Polynom-Ring(n,L);
pred G is_Groebner_basis_of I,T means
:: GROEB_1:def 4
G-Ideal = I & PolyRedRel(G,T) is locally-confluent;
end;
theorem :: GROEB_1:21
for n being Element of NAT, T being connected admissible TermOrder of
n, L being Abelian add-associative right_complementable right_zeroed
commutative associative well-unital distributive almost_left_invertible non
degenerated non empty doubleLoopStr, G,P being non empty Subset of
Polynom-Ring(n,L) st G is_Groebner_basis_of P,T holds PolyRedRel(G,T) is
Completion of PolyRedRel(P,T);
theorem :: GROEB_1:22
for n being Element of NAT, T being connected admissible TermOrder of
n, L being Abelian add-associative right_complementable right_zeroed
commutative associative well-unital distributive almost_left_invertible non
degenerated non empty doubleLoopStr, p,q being Element of Polynom-Ring(n,L),
G being non empty Subset of Polynom-Ring(n,L) st G is_Groebner_basis_wrt T
holds p,q are_congruent_mod G-Ideal iff nf(p,PolyRedRel(G,T)) = nf(q,PolyRedRel
(G,T));
theorem :: GROEB_1:23
for n being Element of NAT, T being connected admissible TermOrder of
n, L being add-associative right_complementable right_zeroed commutative
associative well-unital distributive Abelian almost_left_invertible non
degenerated non empty doubleLoopStr, f being Polynomial of n,L, P being non
empty Subset of Polynom-Ring(n,L) st P is_Groebner_basis_wrt T holds f in P
-Ideal iff PolyRedRel(P,T) reduces f,0_(n,L);
theorem :: GROEB_1:24 :: theorem 5.38 (o) ==> (i), p. 207
for n being Element of NAT, T being connected admissible
TermOrder of n, L being add-associative right_complementable right_zeroed
commutative associative well-unital distributive Abelian almost_left_invertible
non degenerated non empty doubleLoopStr, I being Subset of Polynom-Ring(n,L),
G being non empty Subset of Polynom-Ring(n,L) holds G is_Groebner_basis_of I,T
implies (for f being Polynomial of n,L st f in I holds PolyRedRel(G,T) reduces
f,0_(n,L));
theorem :: GROEB_1:25 :: theorem 5.38 (i) ==> (ii), p. 207
for n being Ordinal, T being connected TermOrder of n, L being
add-associative right_complementable right_zeroed commutative associative
well-unital distributive almost_left_invertible non trivial doubleLoopStr, G,
I being Subset of Polynom-Ring(n,L) holds (for f being Polynomial of n,L st f
in I holds PolyRedRel(G,T) reduces f,0_(n,L)) implies (for f being non-zero
Polynomial of n,L st f in I holds f is_reducible_wrt G,T);
theorem :: GROEB_1:26 :: theorem 5.38 (ii) ==> (iii), p. 207
for n being Element of NAT, T being admissible connected
TermOrder of n, L being add-associative right_complementable right_zeroed
commutative associative well-unital distributive Abelian almost_left_invertible
non degenerated non empty doubleLoopStr, I being add-closed left-ideal Subset
of Polynom-Ring(n,L), G being Subset of Polynom-Ring(n,L) st G c= I holds (for
f being non-zero Polynomial of n,L st f in I holds f is_reducible_wrt G,T)
implies (for f being non-zero Polynomial of n,L st f in I holds f
is_top_reducible_wrt G,T);
theorem :: GROEB_1:27 :: theorem 5.38 (iii) ==> (iv), p. 207
for n being Ordinal, T being connected TermOrder of n, L being
add-associative right_complementable right_zeroed commutative associative
well-unital distributive almost_left_invertible non trivial doubleLoopStr, G,
I being Subset of Polynom-Ring(n,L) holds (for f being non-zero Polynomial of n
,L st f in I holds f is_top_reducible_wrt G,T) implies (for b being bag of n st
b in HT(I,T) ex b9 being bag of n st b9 in HT(G,T) & b9 divides b);
theorem :: GROEB_1:28 :: theorem 5.38 (iv) ==> (v), p. 207
for n being Ordinal, T being connected TermOrder of n, L being
add-associative right_complementable right_zeroed commutative associative
well-unital distributive almost_left_invertible non trivial doubleLoopStr, G,
I being Subset of Polynom-Ring(n,L) holds (for b being bag of n st b in HT(I,T)
ex b9 being bag of n st b9 in HT(G,T) & b9 divides b) implies HT(I,T) c=
multiples(HT(G,T));
theorem :: GROEB_1:29 :: theorem 5.38 (v) ==> (o), p. 207
for n being Element of NAT, T being connected admissible
TermOrder of n, L being Abelian add-associative right_complementable
right_zeroed commutative associative well-unital distributive
almost_left_invertible non degenerated non empty doubleLoopStr, I being
add-closed left-ideal non empty Subset of Polynom-Ring(n,L), G being non empty
Subset of Polynom-Ring(n,L) st G c= I holds HT(I,T) c= multiples(HT(G,T))
implies G is_Groebner_basis_of I,T;
begin :: Existence of Groebner Bases
theorem :: GROEB_1:30
for n being Element of NAT, T being connected admissible
TermOrder of n, L being add-associative right_complementable right_zeroed
commutative associative well-unital distributive Abelian almost_left_invertible
non trivial doubleLoopStr holds {0_(n,L)} is_Groebner_basis_of {0_(n,L)},T;
theorem :: GROEB_1:31
for n being Element of NAT, T being connected admissible TermOrder of
n, L being add-associative right_complementable right_zeroed commutative
associative well-unital distributive Abelian almost_left_invertible non
trivial doubleLoopStr, p being Polynomial of n,L holds {p}
is_Groebner_basis_of {p}-Ideal,T;
theorem :: GROEB_1:32
for T being admissible connected TermOrder of {}, L being
add-associative right_complementable right_zeroed commutative associative
well-unital distributive Abelian almost_left_invertible non degenerated non
empty doubleLoopStr, I being add-closed left-ideal non empty Subset of
Polynom-Ring({},L), P being non empty Subset of Polynom-Ring({},L) st P c= I &
P <> {0_({},L)} holds P is_Groebner_basis_of I,T;
theorem :: GROEB_1:33
for n being non empty Ordinal, T being admissible connected TermOrder
of n, L being add-associative right_complementable right_zeroed commutative
associative well-unital distributive almost_left_invertible non degenerated
non empty doubleLoopStr ex P be Subset of Polynom-Ring(n,L) st not(P
is_Groebner_basis_wrt T);
definition :: definition preceeding 5.1, p. 189
let n be Ordinal;
func DivOrder(n) -> Order of Bags n means
:: GROEB_1:def 5
for b1,b2 being bag of n holds [b1,b2] in it iff b1 divides b2;
end;
registration :: theorem 5.2, p. 189
let n be Element of NAT;
cluster RelStr(#Bags n, DivOrder n#) -> Dickson;
end;
theorem :: GROEB_1:34 :: theorem 5.2, p. 189
for n being Element of NAT, N being Subset of RelStr(#Bags n,
DivOrder n#) ex B being finite Subset of Bags n st B is_Dickson-basis_of N,
RelStr(#Bags n, DivOrder n#);
theorem :: GROEB_1:35 :: theorem 5.41, p. 208
for n being Element of NAT, T being connected admissible
TermOrder of n, L being Abelian add-associative right_complementable
right_zeroed commutative associative well-unital distributive
almost_left_invertible non degenerated non empty doubleLoopStr, I being
add-closed left-ideal non empty Subset of Polynom-Ring(n,L) ex G being finite
Subset of Polynom-Ring(n,L) st G is_Groebner_basis_of I,T;
theorem :: GROEB_1:36
for n being Element of NAT, T being connected admissible TermOrder of
n, L being Abelian add-associative right_complementable right_zeroed
commutative associative well-unital distributive almost_left_invertible non
degenerated non empty doubleLoopStr, I being add-closed left-ideal non empty
Subset of Polynom-Ring(n,L) st I <> {0_(n,L)} ex G being finite Subset of
Polynom-Ring(n,L) st G is_Groebner_basis_of I,T & not(0_(n,L) in G);
definition
let n be Ordinal, T be connected TermOrder of n, L be non empty
multLoopStr_0, p be Polynomial of n,L;
pred p is_monic_wrt T means
:: GROEB_1:def 6
HC(p,T) = 1.L;
end;
definition :: definition 5.29, p. 203
let n be Ordinal, T be connected TermOrder of n, L be right_zeroed
add-associative right_complementable commutative associative well-unital
distributive almost_left_invertible non trivial doubleLoopStr, P be
Subset of Polynom-Ring(n,L);
pred P is_reduced_wrt T means
:: GROEB_1:def 7
for p being Polynomial of n,L st p in P
holds p is_monic_wrt T & p is_irreducible_wrt P\{p},T;
end;
notation :: definition 5.29, p. 203
let n be Ordinal, T be connected TermOrder of n, L be right_zeroed
add-associative right_complementable commutative associative well-unital
distributive almost_left_invertible non trivial doubleLoopStr, P be
Subset of Polynom-Ring(n,L);
synonym P is_autoreduced_wrt T for P is_reduced_wrt T;
end;
theorem :: GROEB_1:37 :: lemma 5.42, p. 208
for n being Ordinal, T being admissible connected TermOrder of n
, L being add-associative right_complementable right_zeroed commutative
associative well-unital distributive Abelian almost_left_invertible non
degenerated non empty doubleLoopStr, I being add-closed left-ideal Subset of
Polynom-Ring(n,L), m being Monomial of n,L, f,g being Polynomial of n,L st f in
I & g in I & HM(f,T) = m & HM(g,T) = m holds not(ex p being Polynomial of n,L
st p in I & p < f,T & HM(p,T) = m) & not(ex p being Polynomial of n,L st p in I
& p < g,T & HM(p,T) = m) implies f = g;
theorem :: GROEB_1:38
for n being Element of NAT, T being connected admissible TermOrder of
n, L being Abelian add-associative right_complementable right_zeroed
commutative associative well-unital distributive almost_left_invertible non
degenerated non empty doubleLoopStr, I being add-closed left-ideal non empty
Subset of Polynom-Ring(n,L), G being Subset of Polynom-Ring(n,L), p being
Polynomial of n,L, q being non-zero Polynomial of n,L st p in G & q in G & p <>
q & HT(q,T) divides HT(p,T) holds G is_Groebner_basis_of I,T implies G\{p}
is_Groebner_basis_of I,T;
theorem :: GROEB_1:39 :: theorem 5.43, p. 209
for n being Element of NAT, T being connected admissible TermOrder of
n, L being Abelian add-associative right_complementable right_zeroed
commutative associative well-unital distributive almost_left_invertible non
degenerated non empty doubleLoopStr, I being add-closed left-ideal non empty
Subset of Polynom-Ring(n,L) st I <> {0_ (n,L)} ex G being finite Subset of
Polynom-Ring(n,L) st G is_Groebner_basis_of I,T & G is_reduced_wrt T;
theorem :: GROEB_1:40 :: theorem 5.43, p. 209
for n being Element of NAT, T being connected admissible TermOrder of
n, L being Abelian add-associative right_complementable right_zeroed
commutative associative well-unital distributive almost_left_invertible non
degenerated non empty doubleLoopStr, I being add-closed left-ideal non empty
Subset of Polynom-Ring(n,L), G1,G2 being non empty finite Subset of
Polynom-Ring(n,L) st G1 is_Groebner_basis_of I,T & G1 is_reduced_wrt T & G2
is_Groebner_basis_of I,T & G2 is_reduced_wrt T holds G1 = G2;