# poly() gives polymonial, 
  poly(a,b,c,d,x) gives a*x^3+b*x^2+c*x+d,
  poly(a_ and b_) gives x^2-a*x-b*x+a*b, where a and b are roots of polymonial
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poly(a_,b_,x_):=a*x+b;
poly(a_,b_,c_,x_):=a*x^2+b*x+c;
poly(a_,b_,c_,d_,x_):=a*x^3+b*x^2+c*x+d;
poly(a_,b_,c_,d_,f_,x_):=a*x^4+b*x^3+c*x^2+d*x+f;

poly(a_ and b_, x_) := x^2-a*x-b*x+a*b;
poly(a_ and b_ and c_, x_) := expand((x-a)*(x-b)*(x-c));
poly(a_ and b_,c_, x_) := expand((x-a)*(x-b)*(x-c));
poly(a_ and b_ and c_,d_, x_) := expand((x-a)*(x-b)*(x-c)*(x-d));
poly(a_ and b_ and c_ and d_, x_) := expand((x-a)*(x-b)*(x-c)*(x-d));

poly(n_,x_):=sum(x^k,k,0,n);
poly(0,x_):=1;
poly(1,x_):=x;

poly(a_):=poly(a,x);