function e=sube(e,p)
% subn(e,p): replace in e the equations in p
% example: 
%   syms a b c
%   sube[a,[a==b,b==c])
% by kb

%e=subs(e,lhs(p),rhs(p));   geht manchmal nicht
for n=1:size(p,2)
     e=subs(e,lhs(p(n)),rhs(p(n)));
end
end