|Mathematica Tutorial||Functions »|Tutorials »|More About »|
|Position[list,form]||the positions at which form occurs in list|
|Count[list,form]||the number of times form appears as an element of list|
|MemberQ[list,form]||test whether form is an element of list|
|FreeQ[list,form]||test whether form occurs nowhere in list|
Count counts the number of occurrences of a.