EvaluatedAtAPoint​(AngouriMath.​Entity,​AngouriMath.​Entity,​AngouriMath.​Entity,​System.​Func{AngouriMath.​Entity,​AngouriMath.​Entity.​Variable,​AngouriMath.​Entity},​AngouriMath.​Entity,​AngouriMath.​Entity)

derivative(x^3, x) is 3 x^2, a function of x, whose variable
FreeVariables counts as free for that reason
(https://github.com/asc-community/AngouriMath/issues/1045). Treated as bound, a value put
in for it was dropped: 3 x^2 came back where 3 was owed at x = 1. So
a value for the variable makes the derivative evaluated there,
apply(lambda(x, derivative(x^3, x)), 1), and a value that holds the variable, as
a := x in derivative(a x^2, x), goes in under a fresh variable that the
derivative is then evaluated at, apply(lambda(t, derivative(x t^2, t)), x), which is
2 x^2. Renamed and left at the fresh variable, it was 2 x t.
https://github.com/asc-community/AngouriMath/issues/2189