private Polynomial(ReadOnlyArray <PolynomialTerm> terms)
 {
     _terms = terms;
 }
 private Polynomial(char v)
 {
     _terms = new PolynomialTerm[] { v };
 }
 internal Polynomial(params PolynomialTerm[] terms)
 {
     _terms = PolynomialTerm.Simplify(terms);
 }