private static R tf2 <R>(ExpSym <R> exp, MulSym <R> mexp) => mexp.Mul(exp.Num(3), tf1(exp));
private static R tf1 <R>(ExpSym <R> exp) => exp.Add(exp.Num(8), exp.Neg(exp.Add(exp.Num(1), exp.Num(2))));