Bitwise subtraction

Given the enum:

[Flags]
enum foo
{
a = 1,
b = 2,
c = 4
}

then

foo example = a | b;

If I don't know if foo contains c, previously I have been writing the following

if (example & foo.c == foo.c)
    example  = example ^ foo.c;

Is there a way to do this without checking for the existance of foo.c in example?

As when it comes to additions, I can just do an OR, and if the enum value already exists in example then it doesnt matter.