The die is less than 4 unless it is odd
L:
the die is less than 4
; O:
the die is odd
T
F
L
T
F
O
L ← ¬ O
L ← ¬ O
limit possibilities
ruled out by ψ to those
where φ is
F
extend possibilities
left open by ψ to include
all those where φ is
T