Test LISA-ppo-weakness

LISA LISA-ppo-weakness
(* ppo sequences shouldn't need to end with an Alpha-strong-ppo link.
   This example's cycle is: strong-prop, rd-addr, obs.
*)
{
x=v;
1:r0=u;
}
 P0             | P1           | P2          ;
 r[lderef] r0 x | w[once] y 2  | w[once] u 1 ;
 r[once] r1 r0  | f[mb]        | f[wmb]      ;
 r[once] r2 y   | w[once] x r0 | w[once] y 1 ;
Observed
    y=2; 0:r2=2; 0:r1=0; 0:r0=u;
and y=2; 0:r2=0; 0:r1=0; 0:r0=u;