function 2: and

and:
    description:
        and(ket1, ket2)
        returns |yes> if ket1 and ket2 are |yes>, |no> otherwise.
        now implemented as: ( ket1 && ket2 ) 

    examples:
        and(|yes>, |yes>)
            |yes>

        and(|yes>, |no>)
            |no>

        and(|no>, |no>)
            |no>

    see also:
        or, xor

and:
    description:
        and(ket) input-seq
        applies and(ket, x) for each x in input-seq
        as such, it preserves input-seq structure
        but, because it preserves input-seq structure, it is slower than the above version.

    examples:
        and(|yes>) (|no> . |yes>)
            |no> . |yes>

    see also:
        or, xor