%begin
  %predicate zero(%integer i)
    ! current bug: %true and %false are not implemented but don't complain
    ! %end generates return(0) instead of an error.
    %true %if i=0
    %false
  %end

  %if zero(1) %start
    %signal 15,15
  %finish

  %if zero(0) %start
    %stop
  %finish

%endofprogram