It is sometimes useful to define x as a Symbol

x:Symbol

integrate(x)

(1)

1 x

(2)

But some things can be done with Variables but cannot be done with Symbols

y

(3)

y == 1

y

Compiling body of rule y to compute value of type PositiveInteger

(4)

x := 1

   Cannot convert right-hand side of assignment
   1

      to an object of the type Symbol of the left-hand side.

And this causes an error

x == 1

x

   Internal Error
   Interpreter code generation failed for expression1