and
, which is known, in virtue of its form, to be true for all values of
and
; we have also some other expression, part of the former, which is also known to be true for all values of
and
and
, which is known, in virtue of its form, to be true for all values of
and
; we have also some other expression, part of the former, which is also known to be true for all values of
and