1 | 7. u1: S.car 8. u2: S.car* 9. v: (S.car S.car*)* 10. BL: S.car* 11. t:S.car. mem_f(S.car;t;BL)  ( i: ||v||. 1of(v[i]) = t & mem_f(S.car;s;2of(v[i]))) BL:S.car*.
t:S.car.
mem_f(S.car;t;BL)

( i: || < u1,u2 > .v||. 1of(( < u1,u2 > .v)[i]) = t & mem_f(S.car;s;2of(( < u1,u2 > .v)[i]))) |