ƚ 0Y _ .  &@E & MathType- Times New Roman؟ww w$f-2 2yTimes New Roman؟ww w$f-2 2ySymbol ؟ww w$f-2  y2 : y2  y2 .y2 :.y2 .yTimes New Roman؟ww w$f-2 by & "System$f !-