The sky is blue
The sky is clear.
The sky is blue does not necessarily mean the sky is clear. Likewise, the sky is clear doesn't imply the sky is blue
exists s1 x1.(n_sky(x1) & Theme(s1,x1) & a_blue(s1))
exists s1 x1.(n_sky(x1) & Theme(s1,x1) & a_clear(s1))