| ##### 7.5.10.0. makeUsl Procedure from library `ncalg.lib` (see ncalg_lib). Usage: makeUsl(n,[p]); n an integer, n>1; p an optional integer (field characteristic) Return: ring Purpose: set up the U(sl_n) in the variables ( x(i),y(i),h(i) | i=1..n+1) over the field of char p Note: activate this ring with the `setring` command This presentation of U(sl_n) is the standard one, i.e. positive resp. negative roots are denoted by x(i) resp. y(i) and the Cartan elements are denoted by h(i). The variables are ordered as x(1),...x(n),y(1),...,y(n),h(1),...h(n). Example:
    LIB "ncalg.lib";
    def a=makeUsl(3);
    setring a;
    a;
    ==> // coefficients: QQ considered as a field
    ==> // number of vars : 8
    ==> //        block   1 : ordering dp
    ==> //                  : names    x(1) x(2) x(3) y(1) y(2) y(3) h(1) h(2)
    ==> //        block   2 : ordering C
    ==> // noncommutative relations:
    ==> //    x(2)x(1)=x(1)*x(2)+x(3)
    ==> //    y(1)x(1)=x(1)*y(1)-h(1)
    ==> //    y(3)x(1)=x(1)*y(3)-y(2)
    ==> //    h(1)x(1)=x(1)*h(1)+2*x(1)
    ==> //    h(2)x(1)=x(1)*h(2)-x(1)
    ==> //    y(2)x(2)=x(2)*y(2)-h(2)
    ==> //    y(3)x(2)=x(2)*y(3)+y(1)
    ==> //    h(1)x(2)=x(2)*h(1)-x(2)
    ==> //    h(2)x(2)=x(2)*h(2)+2*x(2)
    ==> //    y(1)x(3)=x(3)*y(1)-x(2)
    ==> //    y(2)x(3)=x(3)*y(2)+x(1)
    ==> //    y(3)x(3)=x(3)*y(3)-h(1)-h(2)
    ==> //    h(1)x(3)=x(3)*h(1)+x(3)
    ==> //    h(2)x(3)=x(3)*h(2)+x(3)
    ==> //    y(2)y(1)=y(1)*y(2)-y(3)
    ==> //    h(1)y(1)=y(1)*h(1)-2*y(1)
    ==> //    h(2)y(1)=y(1)*h(2)+y(1)
    ==> //    h(1)y(2)=y(2)*h(1)+y(2)
    ==> //    h(2)y(2)=y(2)*h(2)-2*y(2)
    ==> //    h(1)y(3)=y(3)*h(1)-y(3)
    ==> //    h(2)y(3)=y(3)*h(2)-y(3)
See also: makeQsl3; makeQso3; makeUg2; makeUgl; makeUsl2.

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