[TYPES] logical relations

[Eijiro Sumii]

Dear all,

Thanks again for the responses - I have received a private message
from Prof. Gordon Plotkin (thanks to Phil) and he confirms that the
_idea_ (using relations) was suggested to him by Mike Gordon but the
_name_ ("logical relations") was his.

Of course, as many people pointed out, this idea itself can be tracked
back much further, but that would be another (much longer) story...!

        Eijiro