*   we can write our own operations!

    *   you can use WeScheme's Recipe button to help with
        this; (it is a version of a Design Recipe,
	an approach to thoughtfully designing functions
	and programs...)

    (define (new-op-name param-var1 param-var1 ...)
        body-expression
    )

*   what if we wanted to write
    functions to help us in filling out premise and
    conclusion columns in a truth table?
    ...we could do that!

p->q
...let's write a function if-then!

    remember its truth table?

    P   Q    P->Q
    -------------
    T   T     T
    T   F     F
    F   T     T
    F   F     T

    *   ONE of SEVERAL ways of approaching this:

        hey, this should only be false if
	P is true AND Q is false

	SO, if it is NOT, then I should get true;

        (not (and p (not q)))

*   NOW that I have if-then,
    I can USE it through the rest of this file/
    this WeScheme window!

    (and I can paste it into others as desired...)

*   see examples from WeScheme for function
    green-party-concl, which uses if-then;