ƚ@ Q[ 9 .  @& & MathType0Times New Roman؟ww wR fu-2 Zxy2 LxyTimes New Roman؟ww wR fu-2 2y2 *4y Times New Roman؟ww wR fu-2 2ySymbol R؟ww wR fu-2 J=y2  -y & "SystemuR fu !-