Can a waiver form be used to determine whether a defendant has entered a guilty plea?

The court may rely upon such a validly executed waiver form in assessing whether a plea is voluntary and in assessing whether defendant [175 Cal.App.3d 926] has waived his constitutional rights. "[A] guilty plea entered through counsel is valid so long as it is accompanied by an adequately documented showing that the defendant was aware of his constitutional rights and knowingly and intelligently waived them...." (Mills v. Municipal Court, supra, 10 Cal.3d 288, 305, 110 Cal.Rptr. 329, 515 P.2d 273.) ⁸