Execute a sequence of forms and return the value of the last one
This macro expands to a corresponding nest of calls of
ACL2 !>:trans1 (progn$ (f1 x) (f2 x) (f3 x)) (PROG2$ (F1 X) (PROG2$ (F2 X) (F3 X))) ACL2 !>:trans1 (progn$ (f1 x) (f2 x)) (PROG2$ (F1 X) (F2 X)) ACL2 !>:trans1 (progn$ (f1 x)) (F1 X) ACL2 !>:trans1 (progn$) NIL ACL2 !>