U real ud ldeal s Udy=pU △m= !- pU=pr(-Mb=DU「(1-p rea PU8-85 u dy d *    0 udy d y U  =   0 udy    0 Udy = U   −     0 0 Udy udy ( )  = −   0 U u dy * U        = −   0 1 dy U u U        = −   0 * 1 dy U u m  real = m  ideal = m  = ( ) * m  real = U  −