Expression 21: "f" equals "f" Subscript, 1 , Baseline minus StartFraction, "f" Subscript, 2 , Baseline Over 2 , EndFraction plus StartFraction, "f" Subscript, 3 , Baseline Over 3 ! , EndFraction minus StartFraction, "f" Subscript, 4 , Baseline Over 4 ! , EndFraction plus StartFraction, "f" Subscript, 5 , Baseline Over 5 ! , EndFraction minus StartFraction, "f" Subscript, 6 , Baseline Over 6 ! , EndFraction plus StartFraction, "f" Subscript, 7 , Baseline Over 7 ! , EndFraction minus StartFraction, "f" Subscript, 8 , Baseline Over 8 ! , EndFraction plus StartFraction, "f" Subscript, 9 , Baseline Over 9 ! , EndFraction minus StartFraction, "f" Subscript, 10 , Baseline Over 10 ! , EndFraction plus positive StartFraction, "f" Subscript, 11 , Baseline Over 11 ! , EndFraction minus StartFraction, "f" Subscript, 12 , Baseline Over 12 ! , EndFractionf=f1−f22+f33!−f44!+f55!−f66!+f77!−f88!+f99!−f1010!++f1111!−f1212!