(a)presume, unless the contrary is proved, that the signature and every other part of such document which purports to be in the handwriting of any particular person or which the court may reasonably assume to have been signed by or to be in the handwriting of, any particular person is in that persons' handwriting and in the case of a document executed or attested, that it was executed or attested by the person by whom it purports to have been so executed or attested;
