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IsDefined

check if an expression has been defined
Syntax
          
IsDefined(E)

where E is a CoCoA expression.

          

Description
This function returns True if E is defined, otherwise it returns false. Typically, it is used to check if a name has already been assigned.

NOTE: this function used to be named Defined.

Example
  IsDefined(MyVariable);
False
-------------------------------
  MyVariable := 3;
  IsDefined(MyVariable);
True
-------------------------------