The problem probably doesn't exist, I   
   just see, you simple write d(A), and   
   documentation says:   
      
   calculus: default variable is x   
      
   Oki Doki   
      
   Am Sonntag, 14. Januar 2018 03:00:25 UTC+1 schrieb burs...@gmail.com:   
   > So its possible to erroreously call diff(A,X),   
   > where X is not for sure a variable, this is only   
   > detected at runtime and not at compile time?   
   >   
   > Am Sonntag, 14. Januar 2018 02:39:44 UTC+1 schrieb Dr Huang:   
   > > i means the untyped is that usually user do not need to declare data type.   
   > >   
   > > reference math handbook   
   > > www.mathhandbook.com   
      
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