|  |  4.14.3 module operations 
 
+addition (concatenation of the generators and simplification)
*multiplication with ideal or poly (but not `module` * `module`!)
module_expression [int_expression,int_expression]is a module entry, where the first index indicates the row and
the second the column
module_expressions [int_expression]is a vector, where the index indicates the column (generator)
 
Example:
 |  |   ring r=0,(x,y,z),dp;
  module m=[x,y],[0,0,z];
  print(m*(x+y));
==> x2+xy,0,   
==> xy+y2,0,   
==> 0,    xz+yz
  // this is not distributive:
  print(m*x+m*y);
==> x2,0, xy,0,
==> xy,0, y2,0,
==> 0, xz,0, yz
 | 
 
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