theorem Th75:
  {[a,R]} is arr_computation of R
  proof
    reconsider C = {[a,R]} as a-based non empty array;
    C is arr_computation of R
    proof
A1:   dom C = {a} & a in {a} by FUNCT_5:12,TARSKI:def 1; then
      base-C = a by Def4;
      hence C.(base-C) = R by GRFUNC_1:6;
      hereby let b; assume
        b in dom C; then
        a = b by A1,TARSKI:def 1;
        hence C.b is array of O by GRFUNC_1:6;
      end;
      let b; assume
      b in dom C & succ b in dom C; then
      a = b & a = succ b by A1,TARSKI:def 1; then
      a in a by ORDINAL1:6;
      hence thesis;
    end;
    hence thesis;
  end;
