\ begin {align}\ cov (Y, Z\ mid X) & =\ E\ left (Y Z - Y\ E (Z\ mid X) - Z E (Y\ mid X) +\ E (Y\ mid X) E (Z\ mid X)\ biggm| X\ right) =\ E (Y Z\ mid X) -\ E\ left [Y\ E (Z\ mid X)\ media X\ derecha] ...\ begin {align}\ cov (Y, Z\ mid X) & =\ E\ left (Y Z - Y\ E (Z\ mid X) - Z E (Y\ mid X) +\ E (Y\ mid X) E (Z\ mid X)\ biggm| X\ right) =\ E (Y Z\ mid X) -\ E\ left [Y\ E (Z\ mid X)\ media X\ derecha] -\ E\ izquierda [Z\ E (Y\ media X)\ media X\ derecha] +\ E\ izquierda [\ E (Y\ media X)\ E (Z\ media X)\ media X\ derecha]\\ & =\ E\ izquierda (Y Z\ media X\ derecha) -\ E (Y\ media X)\ E (Z\ media X) -\ E (Y\ media X)\ E (Z\ media X) +\ E (Y\ media X)\ E (Z\ media X) =\ E\ izquierda (Y Z\ media X\…
