Section 37-1-312 - Grounds for relief "previously determined" or "waived" defined(a) A ground for relief is "previously determined" if a court of competent jurisdiction has ruled on the merits after a full hearing.(b) A ground for relief is "waived" if the petitioner knowingly and understandingly fails to present it for determination in any proceeding before a court of competent jurisdiction in which the ground could have been presented. There is a rebuttable presumption that a ground for relief not raised in any such proceeding that was held was waived.Acts 1978, ch. 750, § 12; T.C.A., § 37-1712.