theorem
  [!(r1(#)f1+r2(#)f2),x0,x1,x2,x3!] = r1*[!f1,x0,x1,x2,x3!]+r2*[!f2,x0,
  x1,x2,x3!]
proof
  [!(r1(#)f1+r2(#)f2),x0,x1,x2,x3!] = [!(r1(#)f1),x0,x1,x2,x3!] +[!(r2(#)
  f2),x0,x1,x2,x3!] by Th9
    .= r1*[!f1,x0,x1,x2,x3!]+[!(r2(#)f2),x0,x1,x2,x3!] by Th8;
  hence thesis by Th8;
end;
