LIB "tst.lib"; tst_init();
LIB "ncalg.lib";
ring ABP=0,(p4,p5,a,b),dp; //  a commutative ring
def Usl3 = makeUsl(3);
def BIG  = Usl3+ABP;
setring BIG;
poly P4 = 3*x(1)*y(1)+3*x(2)*y(2)+3*x(3)*y(3);
P4 = P4 +h(1)^2+h(1)*h(2)+h(2)^2-3*h(1)-3*h(2);
// P4 is a central element of Usl3 of degree 2
poly P5 = 4*x(1)*y(1) + h(1)^2 - 2*h(1);
// P5 is a central element of the subalgebra of U(sl_3),
// generated by x(1),y(1),h(1)
ideal J = x(1),x(2),h(1)-a,h(2)-b;
// we are interested in the module U(sl_3)/J,
// which depends on parameters a,b
ideal I = p4-P4, p5-P5;
ideal K = I, J;
ideal E = eliminate(K,x(1)*x(2)*x(3)*y(1)*y(2)*y(3)*h(1)*h(2));
E; // this is the ideal of central characters in ABP
// what are the characters on nonzero a,b?
ring abP = (0,a,b),(p4,p5),dp;
ideal abE = imap(BIG, E);
option(redSB);
option(redTail);
abE = std(abE);
// here come characters (indeed, we have only one)
// that is a maximal ideal in K[p4,p5]
abE;
tst_status(1);$