eqBox (Let _ p t,s) c =
    do s' <- evalProg (p,s)
       eqBox (t,s') c
eqBox (Let _ p t,s) c =
    do s' <- evalProg (p,s)
       eqBox (t,s') c
eqBox (Let _ p t,s) c =
    do s' <- evalProg (p,s)
       eqBox (t,s') c