# Further examples from Wester’s paper#

These are all the problems at http://yacas.sourceforge.net/essaysmanual.html

They come from the 1994 paper “Review of CAS mathematical capabilities”, by Michael Wester, who put forward 123 problems that a reasonable computer algebra system should be able to solve and tested the then current versions of various commercial CAS on this list. Sage can do most of the problems natively now, i.e., with no explicit calls to Maxima or other systems.

```sage: # (YES) factorial of 50, and factor it
sage: factorial(50)
30414093201713378043612608166064768844377641568960512000000000000
sage: factor(factorial(50))
2^47 * 3^22 * 5^12 * 7^8 * 11^4 * 13^3 * 17^2 * 19^2 * 23^2 * 29 * 31 * 37 * 41 * 43 * 47
```
```sage: # (YES) 1/2+...+1/10 = 4861/2520
sage: sum(1/n for n in range(2,10+1)) == 4861/2520
True
```
```sage: # (YES) Evaluate  e^(Pi*Sqrt(163)) to 50 decimal digits
sage: a = e^(pi*sqrt(163)); a
e^(sqrt(163)*pi)
sage: RealField(150)(a)
2.6253741264076874399999999999925007259719820e17
```
```sage: # (YES) Evaluate the Bessel function J numerically at z=1+I.
sage: bessel_J(2, 1+I).n()
0.0415798869439621 + 0.247397641513306*I
```
```sage: # (YES) Obtain period of decimal fraction 1/7=0.(142857).
sage: a = 1/7
sage: a
1/7
sage: a.period()
6
```
```sage: # (YES) Continued fraction of 3.1415926535
sage: a = 3.1415926535
sage: continued_fraction(a)
[3; 7, 15, 1, 292, 1, 1, 6, 2, 13, 4]
```
```sage: # (YES) Sqrt(2*Sqrt(3)+4)=1+Sqrt(3).
sage: # The Maxima backend equality checker does this;
sage: # note the equality only holds for one choice of sign,
sage: # but Maxima always chooses the "positive" one
sage: a = sqrt(2*sqrt(3) + 4); b = 1 + sqrt(3)
sage: float(a-b)
0.0
sage: bool(a == b)
True
sage: # We can, of course, do this in a quadratic field
sage: asqr = 2*sqrt3 + 4
sage: b = 1+sqrt3
sage: asqr == b^2
True
```
```sage: # (YES) Sqrt(14+3*Sqrt(3+2*Sqrt(5-12*Sqrt(3-2*Sqrt(2)))))=3+Sqrt(2).
sage: a = sqrt(14+3*sqrt(3+2*sqrt(5-12*sqrt(3-2*sqrt(2)))))
sage: b = 3+sqrt(2)
sage: a, b
(sqrt(3*sqrt(2*sqrt(-12*sqrt(-2*sqrt(2) + 3) + 5) + 3) + 14), sqrt(2) + 3)
sage: bool(a==b)
True
sage: abs(float(a-b)) < 1e-10
True
sage: # 2*Infinity-3=Infinity.
sage: 2*infinity-3 == infinity
True
```
```sage: # (YES) Standard deviation of the sample (1, 2, 3, 4, 5).
sage: v = vector(RDF, 5, [1,2,3,4,5])
sage: v.standard_deviation()
1.5811388300841898
```
```sage: # (NO) Hypothesis testing with t-distribution.
sage: # (NO) Hypothesis testing with chi^2 distribution
sage: # (But both are included in Scipy and R)
```
```sage: # (YES) (x^2-4)/(x^2+4*x+4)=(x-2)/(x+2).
sage: R.<x> = QQ[]
sage: (x^2-4)/(x^2+4*x+4) == (x-2)/(x+2)
True
sage: restore('x')
```
```sage: # (YES -- Maxima doesn't immediately consider them
sage: # equal, but simplification shows that they are)
sage: # (Exp(x)-1)/(Exp(x/2)+1)=Exp(x/2)-1.
sage: f = (exp(x)-1)/(exp(x/2)+1)
sage: g = exp(x/2)-1
sage: f
(e^x - 1)/(e^(1/2*x) + 1)
sage: g
e^(1/2*x) - 1
e^(1/2*x) - 1
sage: g
e^(1/2*x) - 1
sage: f(x=10.0).n(53), g(x=10.0).n(53)
(147.413159102577, 147.413159102577)
sage: bool(f == g)
True
```
```sage: # (YES) Expand (1+x)^20, take derivative and factorize.
sage: # first do it using algebraic polys
sage: R.<x> = QQ[]
sage: f = (1+x)^20; f
x^20 + 20*x^19 + 190*x^18 + 1140*x^17 + 4845*x^16 + 15504*x^15 + 38760*x^14 + 77520*x^13 + 125970*x^12 + 167960*x^11 + 184756*x^10 + 167960*x^9 + 125970*x^8 + 77520*x^7 + 38760*x^6 + 15504*x^5 + 4845*x^4 + 1140*x^3 + 190*x^2 + 20*x + 1
sage: deriv = f.derivative()
sage: deriv
20*x^19 + 380*x^18 + 3420*x^17 + 19380*x^16 + 77520*x^15 + 232560*x^14 + 542640*x^13 + 1007760*x^12 + 1511640*x^11 + 1847560*x^10 + 1847560*x^9 + 1511640*x^8 + 1007760*x^7 + 542640*x^6 + 232560*x^5 + 77520*x^4 + 19380*x^3 + 3420*x^2 + 380*x + 20
sage: deriv.factor()
(20) * (x + 1)^19
sage: restore('x')
sage: # next do it symbolically
sage: var('y')
y
sage: f = (1+y)^20; f
(y + 1)^20
sage: g = f.expand(); g
y^20 + 20*y^19 + 190*y^18 + 1140*y^17 + 4845*y^16 + 15504*y^15 + 38760*y^14 + 77520*y^13 + 125970*y^12 + 167960*y^11 + 184756*y^10 + 167960*y^9 + 125970*y^8 + 77520*y^7 + 38760*y^6 + 15504*y^5 + 4845*y^4 + 1140*y^3 + 190*y^2 + 20*y + 1
sage: deriv = g.derivative(); deriv
20*y^19 + 380*y^18 + 3420*y^17 + 19380*y^16 + 77520*y^15 + 232560*y^14 + 542640*y^13 + 1007760*y^12 + 1511640*y^11 + 1847560*y^10 + 1847560*y^9 + 1511640*y^8 + 1007760*y^7 + 542640*y^6 + 232560*y^5 + 77520*y^4 + 19380*y^3 + 3420*y^2 + 380*y + 20
sage: deriv.factor()
20*(y + 1)^19
```
```sage: # (YES) Factorize x^100-1.
sage: factor(x^100-1)
(x^40 - x^30 + x^20 - x^10 + 1)*(x^20 + x^15 + x^10 + x^5 + 1)*(x^20 - x^15 + x^10 - x^5 + 1)*(x^8 - x^6 + x^4 - x^2 + 1)*(x^4 + x^3 + x^2 + x + 1)*(x^4 - x^3 + x^2 - x + 1)*(x^2 + 1)*(x + 1)*(x - 1)
sage: # Also, algebraically
sage: x = polygen(QQ)
sage: factor(x^100 - 1)
(x - 1) * (x + 1) * (x^2 + 1) * (x^4 - x^3 + x^2 - x + 1) * (x^4 + x^3 + x^2 + x + 1) * (x^8 - x^6 + x^4 - x^2 + 1) * (x^20 - x^15 + x^10 - x^5 + 1) * (x^20 + x^15 + x^10 + x^5 + 1) * (x^40 - x^30 + x^20 - x^10 + 1)
sage: restore('x')
```
```sage: # (YES) Factorize  x^4-3*x^2+1 in the field of rational numbers extended by roots of  x^2-x-1.
sage: x = polygen(ZZ, 'x')
sage: k.< a> = NumberField(x^2 - x -1)
sage: R.< y> = k[]
sage: f = y^4 - 3*y^2 + 1
sage: f
y^4 - 3*y^2 + 1
sage: factor(f)
(y - a) * (y - a + 1) * (y + a - 1) * (y + a)
```
```sage: # (YES) Factorize  x^4-3*x^2+1 mod 5.
sage: k.< x > = GF(5) [ ]
sage: f = x^4 - 3*x^2 + 1
sage: f.factor()
(x + 2)^2 * (x + 3)^2
sage: # Alternatively, from symbol x as follows:
sage: reset('x')
sage: f = x^4 - 3*x^2 + 1
sage: f.polynomial(GF(5)).factor()
(x + 2)^2 * (x + 3)^2
```
```sage: # (YES) Partial fraction decomposition of (x^2+2*x+3)/(x^3+4*x^2+5*x+2)
sage: f = (x^2+2*x+3)/(x^3+4*x^2+5*x+2); f
(x^2 + 2*x + 3)/(x^3 + 4*x^2 + 5*x + 2)
sage: f.partial_fraction()
3/(x + 2) - 2/(x + 1) + 2/(x + 1)^2
```
```sage: # (YES) Assuming  x>=y,  y>=z,  z>=x, deduce  x=z.
sage: forget()
sage: var('x,y,z')
(x, y, z)
sage: assume(x>=y, y>=z,z>=x)
sage: bool(x==z)
True
```
```sage: # (YES) Assuming x>y, y>0, deduce 2*x^2>2*y^2.
sage: forget()
sage: assume(x>y, y>0)
sage: sorted(assumptions())
[x > y, y > 0]
sage: bool(2*x^2 > 2*y^2)
True
sage: forget()
sage: assumptions()
[]
```
```sage: # (NO) Solve the inequality Abs(x-1)>2.
sage: # Maxima doesn't solve inequalities
sage: # (but some Maxima packages do):
sage: eqn = abs(x-1) > 2
sage: eqn.solve(x)
[[x < -1], [3 < x]]
```
```sage: # (NO) Solve the inequality (x-1)*...*(x-5)<0.
sage: eqn = prod(x-i for i in range(1,5 +1)) < 0
sage: # but don't know how to solve
sage: eqn.solve(x)
[[x < 1], [x > 2, x < 3], [x > 4, x < 5]]
```
```sage: # (YES) Cos(3*x)/Cos(x)=Cos(x)^2-3*Sin(x)^2 or similar equivalent combination.
sage: f = cos(3*x)/cos(x)
sage: g = cos(x)^2 - 3*sin(x)^2
sage: h = f-g
sage: h.trig_simplify()
0
```
```sage: # (YES) Cos(3*x)/Cos(x)=2*Cos(2*x)-1.
sage: f = cos(3*x)/cos(x)
sage: g = 2*cos(2*x) - 1
sage: h = f-g
sage: h.trig_simplify()
0
```
```sage: # (GOOD ENOUGH) Define rewrite rules to match  Cos(3*x)/Cos(x)=Cos(x)^2-3*Sin(x)^2.
sage: # Sage has no notion of "rewrite rules", but
sage: # it can simplify both to the same thing.
sage: (cos(3*x)/cos(x)).simplify_full()
4*cos(x)^2 - 3
sage: (cos(x)^2-3*sin(x)^2).simplify_full()
4*cos(x)^2 - 3
```
```sage: # (YES) Sqrt(997)-(997^3)^(1/6)=0
sage: a = sqrt(997) - (997^3)^(1/6)
sage: a.simplify()
0
sage: bool(a == 0)
True
```
```sage: # (YES) Sqrt(99983)-99983^3^(1/6)=0
sage: a = sqrt(99983) - (99983^3)^(1/6)
sage: bool(a==0)
True
sage: float(a)
1.1368683772...e-13
sage: 13*7691
99983
```
```sage: # (YES) (2^(1/3) + 4^(1/3))^3 - 6*(2^(1/3) + 4^(1/3))-6 = 0
sage: a = (2^(1/3) + 4^(1/3))^3 - 6*(2^(1/3) + 4^(1/3)) - 6; a
(4^(1/3) + 2^(1/3))^3 - 6*4^(1/3) - 6*2^(1/3) - 6
sage: bool(a==0)
True
sage: abs(float(a)) < 1e-10
True
```

Or we can do it using number fields.

```sage: reset('x')
sage: k.<b> = NumberField(x^3-2)
sage: a = (b  + b^2)^3 - 6*(b  + b^2) - 6
sage: a
0
```
```sage: # (NO, except numerically) Ln(Tan(x/2+Pi/4))-ArcSinh(Tan(x))=0
# Sage uses the Maxima convention when comparing symbolic expressions and
# returns True only when it can prove equality. Thus, in this case, we get
# False even though the equality holds.
sage: f = log(tan(x/2 + pi/4)) - arcsinh(tan(x))
sage: bool(f == 0)
False
sage: [abs(float(f(x=i/10))) < 1e-15 for i in range(1,5)]
[True, True, True, True]
sage: # Numerically, the expression Ln(Tan(x/2+Pi/4))-ArcSinh(Tan(x))=0 and its derivative at x=0 are zero.
sage: g = f.derivative()
sage: abs(float(f(x=0))) < 1e-10
True
sage: abs(float(g(x=0))) < 1e-10
True
sage: g
-sqrt(tan(x)^2 + 1) + 1/2*(tan(1/4*pi + 1/2*x)^2 + 1)/tan(1/4*pi + 1/2*x)
```
```sage: # (NO) Ln((2*Sqrt(r) + 1)/Sqrt(4*r 4*Sqrt(r) 1))=0.
sage: var('r')
r
sage: f = log( (2*sqrt(r) + 1) / sqrt(4*r  + 4*sqrt(r) +  1)); f
log((2*sqrt(r) + 1)/sqrt(4*r + 4*sqrt(r) + 1))
sage: bool(f == 0)
False
sage: [abs(float(f(r=i))) < 1e-10 for i in [0.1,0.3,0.5]]
[True, True, True]
```
```sage: # (NO)
sage: # (4*r+4*Sqrt(r)+1)^(Sqrt(r)/(2*Sqrt(r)+1))*(2*Sqrt(r)+1)^(2*Sqrt(r)+1)^(-1)-2*Sqrt(r)-1=0, assuming r>0.
sage: assume(r>0)
sage: f = (4*r+4*sqrt(r)+1)^(sqrt(r)/(2*sqrt(r)+1))*(2*sqrt(r)+1)^(2*sqrt(r)+1)^(-1)-2*sqrt(r)-1
sage: f
(4*r + 4*sqrt(r) + 1)^(sqrt(r)/(2*sqrt(r) + 1))*(2*sqrt(r) + 1)^(1/(2*sqrt(r) + 1)) - 2*sqrt(r) - 1
sage: bool(f == 0)
False
sage: [abs(float(f(r=i))) < 1e-10 for i in [0.1,0.3,0.5]]
[True, True, True]
```
```sage: # (YES) Obtain real and imaginary parts of Ln(3+4*I).
sage: a = log(3+4*I); a
log(4*I + 3)
sage: a.real()
log(5)
sage: a.imag()
arctan(4/3)
```
```sage: # (YES) Obtain real and imaginary parts of Tan(x+I*y)
sage: z = var('z')
sage: a = tan(z); a
tan(z)
sage: a.real()
sin(2*real_part(z))/(cos(2*real_part(z)) + cosh(2*imag_part(z)))
sage: a.imag()
sinh(2*imag_part(z))/(cos(2*real_part(z)) + cosh(2*imag_part(z)))
```
```sage: # (YES) Simplify Ln(Exp(z)) to z for -Pi<Im(z)<=Pi.
sage: # Unfortunately (?), Maxima does this even without
sage: # any assumptions.
sage: # We *would* use assume(-pi < imag(z))
sage: # and assume(imag(z) <= pi)
sage: f = log(exp(z)); f
log(e^z)
sage: f.simplify()
z
sage: forget()
```
```sage: # (YES) Assuming Re(x)>0, Re(y)>0, deduce x^(1/n)*y^(1/n)-(x*y)^(1/n)=0.
sage: # Maxima 5.26 has different behaviours depending on the current
sage: # domain.
sage: # To stick with the behaviour of previous versions, the domain is set
sage: # to 'real' in the following.
sage: # See Issue #10682 for further details.
sage: n = var('n')
sage: f = x^(1/n)*y^(1/n)-(x*y)^(1/n)
sage: assume(real(x) > 0, real(y) > 0)
sage: f.simplify()
x^(1/n)*y^(1/n) - (x*y)^(1/n)
sage: maxima = sage.calculus.calculus.maxima
sage: maxima.set('domain', 'real') # set domain to real
sage: f.simplify()
0
sage: maxima.set('domain', 'complex') # set domain back to its default value
sage: forget()
```
```sage: # (YES) Transform equations, (x==2)/2+(1==1)=>x/2+1==2.
sage: eq1 = x == 2
sage: eq2 = SR(1) == SR(1)
sage: eq1/2 + eq2
1/2*x + 1 == 2
```
```sage: # (SOMEWHAT) Solve Exp(x)=1 and get all solutions.
sage: # to_poly_solve in Maxima can do this.
sage: solve(exp(x) == 1, x)
[x == 0]
```
```sage: # (SOMEWHAT) Solve Tan(x)=1 and get all solutions.
sage: # to_poly_solve in Maxima can do this.
sage: solve(tan(x) == 1, x)
[x == 1/4*pi]
```
```sage: # (YES) Solve a degenerate 3x3 linear system.
sage: # x+y+z==6,2*x+y+2*z==10,x+3*y+z==10
sage: # First symbolically:
sage: solve([x+y+z==6, 2*x+y+2*z==10, x+3*y+z==10], x,y,z)
[[x == -r1 + 4, y == 2, z == r1]]
```
```sage: # (YES) Invert a 2x2 symbolic matrix.
sage: # [[a,b],[1,a*b]]
sage: # Using multivariate poly ring -- much nicer
sage: R.<a,b> = QQ[]
sage: m = matrix(2,2,[a,b,  1, a*b])
sage: zz = m^(-1)
sage: zz
[     a/(a^2 - 1)   (-1)/(a^2 - 1)]
[(-1)/(a^2*b - b)    a/(a^2*b - b)]
```
```sage: # (YES) Compute and factor the determinant of the 4x4 Vandermonde matrix in a, b, c, d.
sage: var('a,b,c,d')
(a, b, c, d)
sage: m = matrix(SR, 4, 4, [[z^i for i in range(4)] for z in [a,b,c,d]])
sage: m
[  1   a a^2 a^3]
[  1   b b^2 b^3]
[  1   c c^2 c^3]
[  1   d d^2 d^3]
sage: d = m.determinant()
sage: d.factor()
(a - b)*(a - c)*(a - d)*(b - c)*(b - d)*(c - d)
```
```sage: # (YES) Compute and factor the determinant of the 4x4 Vandermonde matrix in a, b, c, d.
sage: # Do it instead in a multivariate ring
sage: R.<a,b,c,d> = QQ[]
sage: m = matrix(R, 4, 4, [[z^i for i in range(4)] for z in [a,b,c,d]])
sage: m
[  1   a a^2 a^3]
[  1   b b^2 b^3]
[  1   c c^2 c^3]
[  1   d d^2 d^3]
sage: d = m.determinant()
sage: d
a^3*b^2*c - a^2*b^3*c - a^3*b*c^2 + a*b^3*c^2 + a^2*b*c^3 - a*b^2*c^3 - a^3*b^2*d + a^2*b^3*d + a^3*c^2*d - b^3*c^2*d - a^2*c^3*d + b^2*c^3*d + a^3*b*d^2 - a*b^3*d^2 - a^3*c*d^2 + b^3*c*d^2 + a*c^3*d^2 - b*c^3*d^2 - a^2*b*d^3 + a*b^2*d^3 + a^2*c*d^3 - b^2*c*d^3 - a*c^2*d^3 + b*c^2*d^3
sage: d.factor()
(-1) * (c - d) * (-b + c) * (b - d) * (-a + c) * (-a + b) * (a - d)
```
```sage: # (YES) Find the eigenvalues of a 3x3 integer matrix.
sage: m = matrix(QQ, 3, [5,-3,-7, -2,1,2, 2,-3,-4])
sage: m.eigenspaces_left()
[
(3, Vector space of degree 3 and dimension 1 over Rational Field
User basis matrix:
[ 1  0 -1]),
(1, Vector space of degree 3 and dimension 1 over Rational Field
User basis matrix:
[ 1  1 -1]),
(-2, Vector space of degree 3 and dimension 1 over Rational Field
User basis matrix:
[0 1 1])
]
```
```sage: # (YES) Verify some standard limits found by L'Hopital's rule:
sage: #   Verify(Limit(x,Infinity) (1+1/x)^x, Exp(1));
sage: #   Verify(Limit(x,0) (1-Cos(x))/x^2, 1/2);
sage: limit( (1+1/x)^x, x = oo)
e
sage: limit( (1-cos(x))/(x^2), x = 1/2)
-4*cos(1/2) + 4
```
```sage: # (OK-ish) D(x)Abs(x)
sage: #    Verify(D(x) Abs(x), Sign(x));
sage: diff(abs(x))
1/2*(x + conjugate(x))/abs(x)
sage: _.simplify_full()
x/abs(x)
sage: _ = var('x', domain='real')
sage: diff(abs(x))
x/abs(x)
sage: forget()
```
```sage: # (YES) (Integrate(x)Abs(x))=Abs(x)*x/2
sage: integral(abs(x), x)
1/2*x*abs(x)
```
```sage: #  (YES) Compute derivative of Abs(x), piecewise defined.
sage: #     Verify(D(x)if(x<0) (-x) else x,
sage: #        Simplify(if(x<0) -1 else 1))
Piecewise defined function with 2 parts, [[(-10, 0), -1], [(0, 10), 1]]
sage: #  (NOT really) Integrate Abs(x), piecewise defined.
sage: #      Verify(Simplify(Integrate(x)
sage: #        if(x<0) (-x) else x),
sage: #        Simplify(if(x<0) (-x^2/2) else x^2/2));
sage: f = piecewise([ ((-10,0), -x), ((0,10), x)])
sage: f.integral(definite=True)
100
```
```sage: # (YES) Taylor series of 1/Sqrt(1-v^2/c^2) at v=0.
sage: var('v,c')
(v, c)
sage: taylor(1/sqrt(1-v^2/c^2), v, 0, 7)
1/2*v^2/c^2 + 3/8*v^4/c^4 + 5/16*v^6/c^6 + 1
```
```sage: # (OK-ish) (Taylor expansion of Sin(x))/(Taylor expansion of Cos(x)) = (Taylor expansion of Tan(x)).
sage: #      TestYacas(Taylor(x,0,5)(Taylor(x,0,5)Sin(x))/
sage: #        (Taylor(x,0,5)Cos(x)), Taylor(x,0,5)Tan(x));
sage: f = taylor(sin(x), x, 0, 8)
sage: g = taylor(cos(x), x, 0, 8)
sage: h = taylor(tan(x), x, 0, 8)
sage: f = f.power_series(QQ)
sage: g = g.power_series(QQ)
sage: h = h.power_series(QQ)
sage: f - g*h
O(x^8)
```
```sage: # (YES) Taylor expansion of Ln(x)^a*Exp(-b*x) at x=1.
sage: a,b = var('a,b')
sage: taylor(log(x)^a*exp(-b*x), x, 1, 3)
-1/48*(a^3*(x - 1)^a + a^2*(6*b + 5)*(x - 1)^a + 8*b^3*(x - 1)^a + 2*(6*b^2 + 5*b + 3)*a*(x - 1)^a)*(x - 1)^3*e^(-b) + 1/24*(3*a^2*(x - 1)^a + a*(12*b + 5)*(x - 1)^a + 12*b^2*(x - 1)^a)*(x - 1)^2*e^(-b) - 1/2*(a*(x - 1)^a + 2*b*(x - 1)^a)*(x - 1)*e^(-b) + (x - 1)^a*e^(-b)
```
```sage: # (YES) Taylor expansion of Ln(Sin(x)/x) at x=0.
sage: taylor(log(sin(x)/x), x, 0, 10)
-1/467775*x^10 - 1/37800*x^8 - 1/2835*x^6 - 1/180*x^4 - 1/6*x^2
```
```sage: # (NO) Compute n-th term of the Taylor series of Ln(Sin(x)/x) at x=0.
sage: # need formal functions
```
```sage: # (NO) Compute n-th term of the Taylor series of Exp(-x)*Sin(x) at x=0.
sage: # (Sort of, with some work)
sage: # Solve x=Sin(y)+Cos(y) for y as Taylor series in x at x=1.
sage: #      TestYacas(InverseTaylor(y,0,4) Sin(y)+Cos(y),
sage: #        (y-1)+(y-1)^2/2+2*(y-1)^3/3+(y-1)^4);
sage: #       Note that InverseTaylor does not give the series in terms of x but in terms of y which is semantically
sage: # wrong. But other CAS do the same.
sage: f = sin(y) + cos(y)
sage: g = f.taylor(y, 0, 10)
sage: h = g.power_series(QQ)
sage: k = (h - 1).reverse()
sage: k
y + 1/2*y^2 + 2/3*y^3 + y^4 + 17/10*y^5 + 37/12*y^6 + 41/7*y^7 + 23/2*y^8 + 1667/72*y^9 + 3803/80*y^10 + O(y^11)
```
```sage: # (OK) Compute Legendre polynomials directly from Rodrigues's formula, P[n]=1/(2^n*n!) *(Deriv(x,n)(x^2-1)^n).
sage: #      P(n,x) := Simplify( 1/(2*n)!! *
sage: #        Deriv(x,n) (x^2-1)^n );
sage: #      TestYacas(P(4,x), (35*x^4)/8+(-15*x^2)/4+3/8);
sage: P = lambda n, x: simplify(diff((x^2-1)^n,x,n) / (2^n * factorial(n)))
sage: P(4,x).expand()
35/8*x^4 - 15/4*x^2 + 3/8
```
```sage: # (YES) Define the polynomial p=Sum(i,1,5,a[i]*x^i).
sage: # symbolically
sage: ps = sum(var('a%s'%i)*x^i for i in range(1,6)); ps
a5*x^5 + a4*x^4 + a3*x^3 + a2*x^2 + a1*x
sage: ps.parent()
Symbolic Ring
sage: # algebraically
sage: R = PolynomialRing(QQ,5,names='a')
sage: S.<x> = PolynomialRing(R)
sage: p = S(list(R.gens()))*x; p
a4*x^5 + a3*x^4 + a2*x^3 + a1*x^2 + a0*x
sage: p.parent()
Univariate Polynomial Ring in x over Multivariate Polynomial Ring in a0, a1, a2, a3, a4 over Rational Field
```
```sage: # (YES) Convert the above to Horner's form.
sage: #      Verify(Horner(p, x), ((((a*x+a)*x
sage: #        +a)*x+a)*x+a)*x);
sage: restore('x')
sage: SR(p).horner(x)
((((a4*x + a3)*x + a2)*x + a1)*x + a0)*x
```
```sage: # (NO) Convert the result of problem 127 to Fortran syntax.
sage: #      CForm(Horner(p, x));
```
```sage: # (YES) Verify that True And False=False.
sage: (True and False) is False
True
```
```sage: # (YES) Prove x Or Not x.
sage: for x in [True, False]:
....:    print(x or (not x))
True
True
```
```sage: # (YES) Prove x Or y Or x And y=>x Or y.
sage: for x in [True, False]:
....:   for y in [True, False]:
....:       if x or y or x and y:
....:           if not (x or y):
....:              print("failed!")
```