Singular Manual: defined

  | ### 5.1.18 defined `Syntax:` `defined (` name `)` `Type:` int `Purpose:` returns a value <>0 (TRUE) if there is a user-defined object with this name, and 0 (FALSE) otherwise. A non-zero return value is the level where the object is defined (level 1 denotes the top level, level 2 the level of a first procedure, level 3 the level of a procedure called by a first procedure, etc.). For ring variables and other constants, -1 is returned. `Note:` A local object `m` may be identified by `if (defined(m)==voice)`. `Example:`
        ring r=(0,t),(x,y),dp;
        matrix m[5][6]=x,y,1,2,0,x+y;
        defined(mm);
      ==> 0
        defined(r) and defined(m);
      ==> 1
        defined(m)==voice;   // m is defined in the current level
      ==> 1
        defined(x);
      ==> -1
        defined(z);
      ==> 0
        defined("z");
      ==> -1
        defined(t);
      ==> -1
        defined(42);
      ==> -1
See rvar; voice.

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