theorem
for p being Prime,
    F being p-characteristic Field,
    E being Field st F includes E holds E includes Z/p
proof
let p be Prime, F be p-characteristic Field, E be Field;
assume F includes E;
then F is E-monomorphic by Th71;
then Char E = Char F by Th87 .= p by Def6;
then E is p-characteristic;
hence thesis by Th71;
end;
