src/HOL/Real_Asymp/multiseries_expansion.ML

                   | _ =>
                       let
                         val _ = if get_verbose ectxt then 
                           writeln "Unsupported occurrence of arctan" else ()
                       in
-                        raise TERM ("Unsupported occurence of arctan", [])
+                        raise TERM ("Unsupported occurrence of arctan", [])
                       end)
               | _ => raise TERM ("Unexpected trim result during expansion of arctan", [])
           end
 
 (* Returns an expansion theorem for a function that is already a basis element *)