De Morgan's laws are rules in logic which state that "not (P or Q)" is equivalent to "(not P) and (not Q)", while "not (P and Q)" is equivalent to "(not P) or (not Q)".
These laws may be expressed formally as follows:
¬(α ∧ β) 
¬α ∨ ¬β
…and:
¬(α ∨ β) ¬α ∧ ¬β
