compound context sp fn: save-as-dot

        save-as-dot["", op1, ... , opn] input-sp
        save-as-dot["", *] input-sp
        Save learn rules as a dot file, so it can be visualized with graphviz.
        The first parameter is the filename to save it to,
        noting the file will be saved to the current directory, even if you specify a path.
        The operators then define which operators to use, * means use all operators.
        input-sp is a list of the kets we want to save as dot files.

        -- Save everything, to the file
        save-as-dot["", *] rel-kets[*]

        -- Save only age and friends for Fred, Sam and Jack, to filename
        save-as-dot["", age, friends] split[" "] |Fred Sam Jack>

    see also: