FreeQ2[expr, {form1, form2, ...}] yields
True if expr does not contain any occurrence
of form1, form2, ... and False otherwise.
FreeQ2[expr, form] is the same as
FreeQ[expr, form].
Overview, SelectFree, SelectNotFree.
FreeQ2[x + f[x] + y, {a, x}]\text{False}
FreeQ2[x + f[x] + y, {a, b}]\text{True}
FreeQ2[x, y]\text{True}
FreeQ2[f[x], f]\text{False}