renamed contravariant relator set_rel to vset_rel, to make room for new covariant relator
header {* Main HOL *}
theory Main
imports Plain Predicate_Compile Nitpick
begin
text {*
Classical Higher-order Logic -- only ``Main'', excluding real and
complex numbers etc.
*}
text {* See further \cite{Nipkow-et-al:2002:tutorial} *}
end