close #41 : Typo Fixed : dereference.adoc

from reference-en pr 635 ( arduino/reference-en#635 )

Author: ThomArmax

Language/Structure/Pointer Access Operators/dereference.adoc

@@ -46,7 +46,7 @@ result = *p;  // 'result' gets the value at the address pointed by 'p'
 
 [float]
 === Notes and Warnings
-Pointers are one of the complicated subjects for beginners in learning C, and it is possible to write the vast majority of Arduino sketches without ever encountering pointers. However for manipulating certain data structures, the use of pointers can simplify the code, and and knowledge of manipulating pointers is handy to have in one's toolkit.
+Pointers are one of the complicated subjects for beginners in learning C, and it is possible to write the vast majority of Arduino sketches without ever encountering pointers. However for manipulating certain data structures, the use of pointers can simplify the code, and knowledge of manipulating pointers is handy to have in one's toolkit.
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