| #### D.2.12.4 defring Procedure from library `ring.lib` (see ring_lib). Usage: defring(ch,n,va,or); ch,va,or=strings, n=integer Return: ring R with characteristic 'ch', ordering 'or' and n variables with names derived from va. If va is a single letter, say va="a", and if n<=26 then a and the following n-1 letters from the alphabet (cyclic order) are taken as variables. If n>26 or if va is a single letter followed by a bracket, say va="T(", the variables are T(1),...,T(n). Note: This proc is useful for defining a ring in a procedure. This proc uses 'execute' or calls a procedure using 'execute'. Example:
    LIB "ring.lib";
    def r=defring("0",5,"u","ls"); r; setring r;"";
    ==> // coefficients: QQ considered as a field
    ==> // number of vars : 5
    ==> //        block   1 : ordering ls
    ==> //                  : names    u v w x y
    ==> //        block   2 : ordering C
    ==>
    def R=defring("(2,A)",10,"x(","(dp(3),ws(1,2,3),ds)"); R; setring R;
    ==> // coefficients: ZZ/2(A) considered as a field
    ==> // number of vars : 10
    ==> //        block   1 : ordering dp
    ==> //                  : names    x(1) x(2) x(3)
    ==> //        block   2 : ordering ws
    ==> //                  : names    x(4) x(5) x(6)
    ==> //                  : weights     1    2    3
    ==> //        block   3 : ordering ds
    ==> //                  : names    x(7) x(8) x(9) x(10)
    ==> //        block   4 : ordering C

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