:: Introduction to Rational Functions
:: by Christoph Schwarzweller
::
:: Received February 8, 2012
:: Copyright (c) 2012-2016 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 ARYTM_3, POLYNOM2, POLYNOM1, ARYTM_1, FUNCT_1, FINSEQ_5,
POLYNOM3, RELAT_1, RLVECT_1, FINSEQ_1, GCD_1, VECTSP_1, CARD_1, ALGSEQ_1,
ALGSTR_1, CARD_3, SGRAPH1, INT_1, FUNCT_4, ALGSTR_0, POLYNOM5, RFINSEQ,
MCART_1, HURWITZ, ZFMISC_1, XBOOLE_0, TARSKI, YELLOW_8, LATTICES,
XCMPLX_0, VECTSP_2, MSALIMIT, STRUCT_0, SUBSET_1, SUPINF_2, NAT_1,
NUMBERS, MESFUNC1, XXREAL_0, RATFUNC1, GROUP_1, FINSEQ_3, BINOP_1,
PARTFUN1, ORDINAL4, ORDINAL1;
notations TARSKI, SUBSET_1, ORDINAL1, XCMPLX_0, PARTFUN1, XXREAL_0, NAT_D,
GROUP_4, FUNCT_7, VECTSP_2, NUMBERS, XTUPLE_0, MCART_1, ALGSTR_0,
ALGSTR_1, VECTSP_1, RLVECT_1, ARYTM_3, RELSET_1, FINSEQ_1, FUNCT_1,
FUNCT_2, GROUP_1, INT_1, NAT_1, FINSEQ_3, VFUNCT_1, RFINSEQ, NORMSP_1,
POLYNOM3, POLYNOM4, FINSEQ_5, POLYNOM5, STRUCT_0, ALGSEQ_1, HURWITZ;
constructors BINOP_1, REAL_1, SQUARE_1, VECTSP_2, POLYNOM4, POLYNOM5,
XTUPLE_0, ALGSTR_2, HURWITZ, FUNCT_4, RELSET_1, ARYTM_3, FUNCT_7,
GROUP_4, NAT_D, VFUNCT_1, RFINSEQ, FINSEQ_5, NAT_1, ALGSEQ_1;
registrations XBOOLE_0, ORDINAL1, RELSET_1, XCMPLX_0, XXREAL_0, XREAL_0,
NAT_1, INT_1, MEMBERED, FINSEQ_1, STRUCT_0, VECTSP_1, ALGSTR_1, GCD_1,
POLYNOM3, POLYNOM4, POLYNOM5, POLYNOM1, FUNCT_2, VFUNCT_1, CARD_1,
RELAT_1, XTUPLE_0;
requirements NUMERALS, SUBSET, REAL, BOOLE, ARITHM;
begin :: Preliminaries
theorem :: RATFUNC1:1
for L being add-associative right_zeroed right_complementable
right-distributive non empty doubleLoopStr
for a being Element of L
for p,q being FinSequence of L
st len p = len q &
for i being Element of NAT st i in dom p holds q/.i = a * (p/.i)
holds Sum q = a * Sum p;
theorem :: RATFUNC1:2
for L being add-associative right_zeroed right_complementable
right-distributive non empty doubleLoopStr
for f being FinSequence of L
for i,j being Element of NAT
st i in dom f & j = i-1 holds Ins(Del(f,i),j,f/.i) = f;
theorem :: RATFUNC1:3
for L being add-associative right_zeroed right_complementable
associative unital right-distributive commutative
non empty doubleLoopStr
for f being FinSequence of L
for i being Element of NAT st i in dom f
holds Product f = (f/.i) * Product Del(f,i);
registration
let L be add-associative right_zeroed right_complementable
well-unital associative left-distributive commutative
almost_left_invertible domRing-like non trivial doubleLoopStr;
let x,y be non zero Element of L;
cluster x / y -> non zero;
end;
registration
cluster domRing-like -> almost_left_cancelable
for add-associative right_zeroed right_complementable
right-distributive non empty doubleLoopStr;
cluster domRing-like -> almost_right_cancelable
for add-associative right_zeroed right_complementable
left-distributive non empty doubleLoopStr;
end;
registration
let x,y be Integer;
cluster max(x,y) -> integer;
cluster min(x,y) -> integer;
end;
theorem :: RATFUNC1:4
for x,y,z being Integer holds max(x+y,x+z) = x + max(y,z);
begin :: More on Polynomials
definition
let L be non empty ZeroStr;
let p be Polynomial of L;
attr p is zero means
:: RATFUNC1:def 1
p = 0_.(L);
attr p is constant means
:: RATFUNC1:def 2
deg p <= 0;
end;
registration
let L be non trivial ZeroStr;
cluster non zero for Polynomial of L;
end;
registration
let L be non empty ZeroStr;
cluster 0_.(L) -> zero constant;
end;
registration
let L be non degenerated multLoopStr_0;
cluster 1_.(L) -> non zero;
end;
registration
let L be non empty multLoopStr_0;
cluster 1_.(L) -> constant;
end;
registration
let L be non empty ZeroStr;
cluster zero -> constant for Polynomial of L;
end;
registration
let L be non empty ZeroStr;
cluster non constant -> non zero for Polynomial of L;
end;
registration
let L be non trivial ZeroStr;
cluster non constant for Polynomial of L;
end;
registration
let L be well-unital non degenerated non empty doubleLoopStr;
let z be Element of L;
let k be Element of NAT;
cluster rpoly(k,z) -> non zero;
end;
registration
let L be add-associative right_zeroed right_complementable distributive
non degenerated doubleLoopStr;
cluster Polynom-Ring(L) -> non degenerated;
end;
registration
let L be domRing-like add-associative right_zeroed right_complementable
distributive non trivial doubleLoopStr;
cluster Polynom-Ring(L) -> domRing-like;
end;
theorem :: RATFUNC1:5
for L being add-associative right_zeroed right_complementable
right-distributive associative non empty doubleLoopStr
for p,q being Polynomial of L
for a being Element of L
holds (a * p) *' q = a * (p *' q);
theorem :: RATFUNC1:6
for L being add-associative right_zeroed right_complementable
right-distributive commutative associative
non empty doubleLoopStr
for p,q being Polynomial of L
for a being Element of L
holds p *' (a * q) = a * (p *' q);
registration
let L be add-associative right_zeroed right_complementable
well-unital commutative associative distributive
almost_left_invertible non trivial doubleLoopStr;
let p be non zero Polynomial of L;
let a be non zero Element of L;
cluster a * p -> non zero;
end;
registration
let L be domRing-like add-associative right_zeroed right_complementable
distributive non trivial doubleLoopStr;
let p1,p2 be non zero Polynomial of L;
cluster p1 *' p2 -> non zero;
end;
theorem :: RATFUNC1:7
for L being add-associative right_zeroed right_complementable distributive
Abelian domRing-like non trivial doubleLoopStr
for p1,p2 being Polynomial of L
for p3 being non zero Polynomial of L
st p1 *' p3 = p2 *' p3 holds p1 = p2;
registration
let L be non trivial ZeroStr;
let p be non zero Polynomial of L;
cluster degree p -> natural;
end;
theorem :: RATFUNC1:8
for L being add-associative right_zeroed right_complementable
unital right-distributive non empty doubleLoopStr
for p being Polynomial of L st deg p = 0
for x being Element of L holds eval(p,x) <> 0.L;
theorem :: RATFUNC1:9
for L being Abelian add-associative right_zeroed right_complementable
well-unital associative commutative distributive
almost_left_invertible non degenerated doubleLoopStr
for p being Polynomial of L
for x being Element of L
holds eval(p,x) = 0.L iff rpoly(1,x) divides p;
theorem :: RATFUNC1:10
for L being Abelian add-associative right_zeroed right_complementable
well-unital associative commutative distributive
almost_left_invertible domRing-like
non degenerated doubleLoopStr
for p,q being Polynomial of L
for x being Element of L st rpoly(1,x) divides (p*'q)
holds rpoly(1,x) divides p or rpoly(1,x) divides q;
theorem :: RATFUNC1:11
for L being Abelian add-associative right_zeroed right_complementable
well-unital associative commutative distributive
almost_left_invertible non degenerated doubleLoopStr
for f being FinSequence of Polynom-Ring(L)
st for i being Nat st i in dom f ex z being Element of L st f.i = rpoly(1,z)
for p being Polynomial of L st p = Product f
holds p <> 0_.(L);
theorem :: RATFUNC1:12
for L being Abelian add-associative right_zeroed right_complementable
well-unital associative commutative distributive
almost_left_invertible domRing-like
non degenerated doubleLoopStr
for f being FinSequence of Polynom-Ring(L)
st for i being Nat st i in dom f ex z being Element of L st f.i = rpoly(1,z)
for p being Polynomial of L st p = Product f
for x being Element of L
holds eval(p,x) = 0.L iff
ex i being Nat st i in dom f & f.i = rpoly(1,x);
begin :: Common Roots of Polynomials
definition
let L be unital non empty doubleLoopStr;
let p1,p2 be Polynomial of L;
let x be Element of L;
pred x is_a_common_root_of p1,p2 means
:: RATFUNC1:def 3
x is_a_root_of p1 & x is_a_root_of p2;
end;
definition
let L be unital non empty doubleLoopStr;
let p1,p2 be Polynomial of L;
pred p1,p2 have_a_common_root means
:: RATFUNC1:def 4
ex x being Element of L st x is_a_common_root_of p1,p2;
end;
notation
let L be unital non empty doubleLoopStr;
let p1,p2 be Polynomial of L;
synonym p1,p2 have_common_roots for p1,p2 have_a_common_root;
antonym p1,p2 have_no_common_roots for p1,p2 have_a_common_root;
end;
theorem :: RATFUNC1:13
for L being Abelian add-associative right_zeroed right_complementable
unital distributive non empty doubleLoopStr
for p being Polynomial of L
for x being Element of L
st x is_a_root_of p holds x is_a_root_of (-p);
theorem :: RATFUNC1:14
for L being Abelian add-associative right_zeroed right_complementable
unital left-distributive non empty doubleLoopStr
for p1,p2 being Polynomial of L
for x being Element of L
st x is_a_common_root_of p1,p2 holds x is_a_root_of p1 + p2;
theorem :: RATFUNC1:15
for L being Abelian add-associative right_zeroed right_complementable
unital distributive non empty doubleLoopStr
for p1,p2 being Polynomial of L
for x being Element of L
st x is_a_common_root_of p1,p2 holds x is_a_root_of -(p1 + p2);
theorem :: RATFUNC1:16
for L being Abelian add-associative right_zeroed right_complementable
unital distributive non empty doubleLoopStr
for p,q being Polynomial of L
for x being Element of L
st x is_a_common_root_of p,q holds x is_a_root_of p+q;
theorem :: RATFUNC1:17
for L being Abelian add-associative right_zeroed right_complementable
well-unital associative commutative distributive
almost_left_invertible non trivial doubleLoopStr
for p1,p2 being Polynomial of L
st p1 divides p2 & p1 is with_roots holds p1,p2 have_common_roots;
definition
let L be unital non empty doubleLoopStr;
let p,q be Polynomial of L;
func Common_Roots(p,q) -> Subset of L equals
:: RATFUNC1:def 5
{ x where x is Element of L : x is_a_common_root_of p,q };
end;
begin :: Normalized Polynomials
definition
let L be non empty ZeroStr;
let p be Polynomial of L;
func Leading-Coefficient(p) -> Element of L equals
:: RATFUNC1:def 6
p.(len p-'1);
end;
notation
let L be non empty ZeroStr;
let p be Polynomial of L;
synonym LC p for Leading-Coefficient(p);
end;
registration
let L be non trivial doubleLoopStr;
let p be non zero Polynomial of L;
cluster LC p -> non zero;
end;
theorem :: RATFUNC1:18
for L being add-associative right_zeroed right_complementable
well-unital commutative associative distributive
almost_left_invertible non empty doubleLoopStr
for p being Polynomial of L
for a being Element of L holds LC(a * p) = a * LC(p);
definition
let L be non empty doubleLoopStr;
let p be Polynomial of L;
attr p is normalized means
:: RATFUNC1:def 7
LC p = 1.L;
end;
registration
let L be add-associative right_zeroed right_complementable
well-unital commutative associative distributive
almost_left_invertible non trivial doubleLoopStr;
let p be non zero Polynomial of L;
cluster (1.L / LC p) * p -> normalized;
end;
registration
let L be Field;
let p be non zero Polynomial of L;
cluster NormPolynomial(p) -> normalized;
end;
begin :: Rational Functions
definition
let L be non trivial multLoopStr_0;
mode rational_function of L -> set means
:: RATFUNC1:def 8
ex p1 being Polynomial of L st
ex p2 being non zero Polynomial of L st it = [p1,p2];
end;
definition
let L be non trivial multLoopStr_0;
let p1 be Polynomial of L;
let p2 be non zero Polynomial of L;
redefine func [p1,p2] -> rational_function of L;
end;
definition
let L be non trivial multLoopStr_0;
let z be rational_function of L;
redefine func z`1 -> Polynomial of L;
redefine func z`2 -> non zero Polynomial of L;
end;
definition
let L be non trivial multLoopStr_0;
let z be rational_function of L;
attr z is zero means
:: RATFUNC1:def 9
z`1 = 0_.(L);
end;
registration
let L be non trivial multLoopStr_0;
cluster non zero for rational_function of L;
end;
theorem :: RATFUNC1:19
for L being non trivial multLoopStr_0
for z being rational_function of L holds z = [z`1,z`2];
definition
let L be add-associative right_zeroed right_complementable distributive
unital non trivial doubleLoopStr;
let z be rational_function of L;
attr z is irreducible means
:: RATFUNC1:def 10
z`1, z`2 have_no_common_roots;
end;
notation
let L be add-associative right_zeroed right_complementable distributive
unital non trivial doubleLoopStr;
let z be rational_function of L;
antonym z is reducible for z is irreducible;
end;
definition
let L be add-associative right_zeroed right_complementable distributive
unital non trivial doubleLoopStr;
let z be rational_function of L;
attr z is normalized means
:: RATFUNC1:def 11
z is irreducible & z`2 is normalized;
end;
registration
let L be add-associative right_zeroed right_complementable distributive
unital non trivial doubleLoopStr;
cluster normalized -> irreducible for rational_function of L;
end;
registration
let L be Abelian add-associative right_zeroed right_complementable
well-unital associative distributive commutative
almost_left_invertible domRing-like non trivial doubleLoopStr;
let z be rational_function of L;
cluster LC(z`2) -> non zero;
end;
definition
let L be Abelian add-associative right_zeroed right_complementable
well-unital associative distributive commutative
almost_left_invertible domRing-like non trivial doubleLoopStr;
let z be rational_function of L;
func NormRationalFunction z -> rational_function of L equals
:: RATFUNC1:def 12
[(1.L / LC(z`2)) * z`1, (1.L / LC(z`2)) * z`2];
end;
notation
let L be Abelian add-associative right_zeroed right_complementable
well-unital associative distributive commutative
almost_left_invertible domRing-like non trivial doubleLoopStr;
let z be rational_function of L;
synonym NormRatF z for NormRationalFunction z;
end;
registration
let L be Abelian add-associative right_zeroed right_complementable
well-unital associative distributive commutative
almost_left_invertible domRing-like non trivial doubleLoopStr;
let z be non zero rational_function of L;
cluster NormRationalFunction z -> non zero;
end;
definition
let L be non degenerated multLoopStr_0;
func 0._(L) -> rational_function of L equals
:: RATFUNC1:def 13
[ 0_.(L), 1_.(L) ];
func 1._(L) -> rational_function of L equals
:: RATFUNC1:def 14
[ 1_.(L), 1_.(L) ];
end;
registration
let L be add-associative right_zeroed right_complementable distributive
associative well-unital non degenerated doubleLoopStr;
cluster 0._(L) -> normalized;
end;
registration
let L be non degenerated multLoopStr_0;
cluster 1._(L) -> non zero;
end;
registration
let L be add-associative right_zeroed right_complementable distributive
associative well-unital non degenerated doubleLoopStr;
cluster 1._(L) -> irreducible;
end;
registration
let L be add-associative right_zeroed right_complementable distributive
associative well-unital non degenerated doubleLoopStr;
cluster irreducible non zero for rational_function of L;
end;
registration
let L be add-associative right_zeroed right_complementable distributive
Abelian associative well-unital non degenerated doubleLoopStr;
let x be Element of L;
cluster [ rpoly(1,x), rpoly(1,x) ] -> reducible non zero
for rational_function of L;
end;
registration
let L be add-associative right_zeroed right_complementable distributive
Abelian associative well-unital non degenerated doubleLoopStr;
cluster reducible non zero for rational_function of L;
end;
registration
let L be add-associative right_zeroed right_complementable distributive
associative well-unital non degenerated doubleLoopStr;
cluster normalized for rational_function of L;
end;
registration
let L be non degenerated multLoopStr_0;
cluster 0._(L) -> zero;
end;
registration
let L be add-associative right_zeroed right_complementable distributive
associative well-unital non degenerated doubleLoopStr;
cluster 1._(L) -> normalized;
end;
definition
let L be domRing-like add-associative right_zeroed right_complementable
distributive non trivial doubleLoopStr;
let p,q be rational_function of L;
func p + q -> rational_function of L equals
:: RATFUNC1:def 15
[ p`1 *' q`2 + p`2 *' q`1, p`2 *' q`2];
end;
definition
let L be domRing-like add-associative right_zeroed right_complementable
distributive non trivial doubleLoopStr;
let p,q be rational_function of L;
func p *' q -> rational_function of L equals
:: RATFUNC1:def 16
[ p`1 *' q`1, p`2 *' q`2];
end;
theorem :: RATFUNC1:20
for L being add-associative right_zeroed right_complementable
well-unital commutative associative distributive
almost_left_invertible non trivial doubleLoopStr
for p being rational_function of L
for a being non zero Element of L
holds [a * p`1, a * p`2] is irreducible iff p is irreducible;
begin
theorem :: RATFUNC1:21
for L being Abelian add-associative right_zeroed right_complementable
well-unital associative distributive commutative
domRing-like non trivial doubleLoopStr
for z being rational_function of L
ex z1 being rational_function of L,
z2 being non zero Polynomial of L
st z = [z2 *' z1`1, z2 *' z1`2] & z1 is irreducible &
ex f being FinSequence of Polynom-Ring(L)
st z2 = Product f &
for i being Element of NAT st i in dom f
ex x being Element of L st x is_a_common_root_of z`1,z`2 &
f.i = rpoly(1,x);
definition
let L be Abelian add-associative right_zeroed right_complementable
well-unital associative distributive commutative
almost_left_invertible domRing-like non trivial doubleLoopStr;
let z be rational_function of L;
func NF z -> rational_function of L means
:: RATFUNC1:def 17
ex z1 being rational_function of L,
z2 being non zero Polynomial of L
st z = [z2 *' z1`1, z2 *' z1`2] & z1 is irreducible &
it = NormRationalFunction z1 &
ex f being FinSequence of Polynom-Ring(L)
st z2 = Product f &
for i being Element of NAT st i in dom f
ex x being Element of L st x is_a_common_root_of z`1,z`2 &
f.i = rpoly(1,x)
if z is non zero otherwise it = 0._(L);
end;
registration
let L be Abelian add-associative right_zeroed right_complementable
well-unital associative distributive commutative
almost_left_invertible domRing-like non trivial doubleLoopStr;
let z be rational_function of L;
cluster NF z -> normalized irreducible;
end;
registration
let L be Abelian add-associative right_zeroed right_complementable
well-unital associative distributive commutative
almost_left_invertible domRing-like non trivial doubleLoopStr;
let z be non zero rational_function of L;
cluster NF z -> non zero;
end;
theorem :: RATFUNC1:22
for L be Abelian add-associative right_zeroed right_complementable
well-unital associative distributive commutative
almost_left_invertible domRing-like non trivial doubleLoopStr
for z be non zero rational_function of L
for z1 being rational_function of L,
z2 being non zero Polynomial of L
st z = [z2 *' z1`1, z2 *' z1`2] & z1 is irreducible &
ex f being FinSequence of Polynom-Ring(L)
st z2 = Product f &
for i being Element of NAT st i in dom f
ex x being Element of L st x is_a_common_root_of z`1,z`2 &
f.i = rpoly(1,x)
holds NF z = NormRationalFunction z1;
theorem :: RATFUNC1:23
for L be Abelian add-associative right_zeroed right_complementable
well-unital associative distributive commutative
almost_left_invertible domRing-like non trivial doubleLoopStr
holds NF 0._(L) = 0._(L);
theorem :: RATFUNC1:24
for L be Abelian add-associative right_zeroed right_complementable
well-unital associative distributive commutative
almost_left_invertible domRing-like non trivial doubleLoopStr
holds NF 1._(L) = 1._(L);
theorem :: RATFUNC1:25
for L being Abelian add-associative right_zeroed right_complementable
well-unital associative distributive commutative
almost_left_invertible domRing-like non trivial doubleLoopStr
for z being irreducible non zero rational_function of L
holds NF z = NormRationalFunction z;
theorem :: RATFUNC1:26
for L be Abelian add-associative right_zeroed right_complementable
well-unital associative distributive commutative
almost_left_invertible domRing-like non trivial doubleLoopStr
for z be rational_function of L
for x being Element of L
holds NF [rpoly(1,x) *' z`1, rpoly(1,x) *' z`2] = NF z;
theorem :: RATFUNC1:27
for L being Abelian add-associative right_zeroed right_complementable
well-unital associative distributive commutative
almost_left_invertible domRing-like non trivial doubleLoopStr
for z being rational_function of L
holds NF (NF z) = NF z;
theorem :: RATFUNC1:28
for L being Abelian add-associative right_zeroed right_complementable
well-unital associative distributive commutative
almost_left_invertible domRing-like non degenerated doubleLoopStr
for z being non zero rational_function of L
holds z is irreducible iff
ex a being Element of L st a <> 0.L & [a * (z`1), a * (z`2)] = NF(z);
begin :: Degree of Rational Functions
definition
let L be Abelian add-associative right_zeroed right_complementable
well-unital associative distributive commutative
almost_left_invertible domRing-like non trivial doubleLoopStr;
let z be rational_function of L;
func degree z -> Integer equals
:: RATFUNC1:def 18
max(degree((NF z)`1),degree((NF z)`2));
end;
notation
let L be Abelian add-associative right_zeroed right_complementable
well-unital associative distributive commutative
almost_left_invertible domRing-like non trivial doubleLoopStr;
let z be rational_function of L;
synonym deg z for degree z;
end;
theorem :: RATFUNC1:29
for L being Abelian add-associative right_zeroed right_complementable
well-unital associative distributive commutative
almost_left_invertible domRing-like non trivial doubleLoopStr
for z being rational_function of L
holds degree(z) <= max(degree(z`1),degree(z`2));
theorem :: RATFUNC1:30
for L being Abelian add-associative right_zeroed right_complementable
well-unital associative distributive commutative
almost_left_invertible domRing-like non trivial doubleLoopStr
for z being non zero rational_function of L
holds z is irreducible iff degree z = max( degree(z`1), degree(z`2) );
begin :: Evaluation of Rational Functions
definition
let L be Field;
let z be rational_function of L;
let x be Element of L;
func eval(z,x) -> Element of L equals
:: RATFUNC1:def 19
eval(z`1,x) / eval(z`2,x);
end;
theorem :: RATFUNC1:31
for L being Field
for x being Element of L holds eval(0._(L),x) = 0.L;
theorem :: RATFUNC1:32
for L being Field
for x being Element of L holds eval(1._(L),x) = 1.L;
theorem :: RATFUNC1:33
for L being Field
for p,q being rational_function of L
for x being Element of L st eval(p`2,x) <> 0.L & eval(q`2,x) <> 0.L
holds eval(p+q,x) = eval(p,x) + eval(q,x);
theorem :: RATFUNC1:34
for L being Field
for p,q being rational_function of L
for x being Element of L st eval(p`2,x) <> 0.L & eval(q`2,x) <> 0.L
holds eval(p*'q,x) = eval(p,x) * eval(q,x);
theorem :: RATFUNC1:35
for L being Field
for p being rational_function of L
for x being Element of L st eval(p`2,x) <> 0.L
holds eval(NormRationalFunction p,x) = eval(p,x);
theorem :: RATFUNC1:36
for L being Field
for p being rational_function of L
for x being Element of L st eval(p`2,x) <> 0.L
holds x is_a_common_root_of p`1,p`2 or eval(NF p,x) = eval(p,x);