function YESNO = isreal(F)
%ISREAL (overloaded)

F = flatten(F);
if isempty(F.clauses)
YESNO = 1;
else
YESNO = 1;
i = 1;
while (i<=length(F.clauses)) & YESNO
Fi = F.clauses{i};
YESNO = YESNO & is(Fi.data,'real');
i = i+1;
end
end