A British guard marches while on duty.
A British guard dances while on duty
One cannot march while on duty and dance simultaneously.
(x)
exists s1 s2 x1 x2 x3 x4.(a_topic(x1) & Time(x1,x4) & n_duty(x4) & Theme(s2,x3) & a_on(s2) & (x1 = x3) & n_dance(x1) & of(x1,x2) & n_guard(x2) & a_british(s1) & Theme(s1,x1))