|  |  7.2.7.2 ring operations (plural) 
+construct a tensor product
 of two  -algebras  and  over the ground field. Let, e.g., 
   ,
and    
be two 
 -algebras, then  is defined to be the algebra 
   ,  ,  . 
 
Concerning the ground fields 
 resp.  of  resp.  , take the
following guidelines for  into consideration: 
One can create a ring usingNeither
 nor  may be  or  .If the characteristic of
 and  differs, then one of them must be  .At most one of
 and  may have parameters.If one of
 and  is an algebraic extension of  it may not be defined by a charstrof type(p^n,a). ring(list), see alsoringlist.
Example:
 |  | LIB "ncalg.lib";
def a = makeUsl2();       // U(sl_2) in e,f,h presentation
ring W0 = 0,(x,d),dp;
def W = Weyl();              // 1st Weyl algebra in x,d
def S = a+W;
setring S;
S;
==> // coefficients: QQ
==> // number of vars : 5
==> //        block   1 : ordering dp
==> //                  : names    e f h
==> //        block   2 : ordering dp
==> //                  : names    x d
==> //        block   3 : ordering C
==> // noncommutative relations:
==> //    fe=ef-h
==> //    he=eh+2e
==> //    hf=fh-2f
==> //    dx=xd+1
 | 
 
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