This article is from the FAQ, by with numerous contributions by others.
If you want to write:
(L: Imp1; Imp2; ... Impi :L)
(which is not implemented), you should instead write:
L: (# do Imp1; Imp2; ... Impi #)
In fact, the (L: ... :L) construct is being considered for exclusion from
the BETA language due to the very simple replacement shown above.
See also L22.