Ring(R:RING):RING

  Use R ::= QQ[x,y,z];
  S ::= ZZ/(3)[a,b];
  Ring(S);
ZZ/(3)[a,b]
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  Ring(R);
QQ[x,y,z]
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  R;  -- same as above, as long as there is no variable with identifier
      -- R in the working memory
QQ[x,y,z]
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  CurrentRing();
QQ[x,y,z]
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  R := 5;  -- a variable with identifier R; now there are two objects
           -- with the identifier R: a variable and a ring
  R;
5
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  Memory();  -- the variables of the working memory
["It", "R"]
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  RingEnvs();  -- the list of rings
["QQ", "QQt", "R", "S", "ZZ"]
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  Ring(R);  -- the ring with identifier R
QQ[x,y,z]
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