infix operators, type 2: %%

 %% :
    description:
        ket1 %% ket2
        return the value of ket1 modulus the value of ket2
        we do our best to preserve categories
        if one ket has a category, and the other doesn't then the result has that category
        if ket1 and ket2 have different categories then return the empty ket |>
        if ket1 and ket2 are 2D, then apply modulus component-wise
        NB: the values for ket1 and ket2 must be integers

    examples:
        |5> %% |3>
            |2>

        |number: 5> %% |3>
            |number: 2>

        |number: 5> %% |page: 3>
            |>

        |3: 7> %% |2: 5>
            |1: 2>

    see also:
        arithmetic, ++ , -- , ** , // , ^^