When I used Mathematica in graduate school, I would ubiquitously specialize a variable and then later "un"specialize it. Specifically, for example, I would write v:= x^3; Then, later, when I wanted the symbol "v" to be left symbolically, I would redefine it with nothing following the definition v:=; I forgot the exact syntax, but it was something like this. But, I cannot find this feature in Maple. Yet I badly need it. Currently, for me to recover the use of a symbolic variable name like 'v', I have to CLOSE DOWN MY DOCUMENT and REOPEN IT! Secondly, in Mathematica, I easily evaluated the "independent" variable to a value

What is the command which returns the length of a list? i.e. length of [1,2,3] is 3 ? More importantly, please tell me where in the help menu this command is listed. Thank you.