u suma zbiorów
n iloczyn zbiorów
k koniunkcja
o zbiór pusty
x ∈ (A u B) k x ∉ (A n B) <=> [x ∈ (A - B) ∨ x ∈ (B - A) ∨ x ∉ (A n B)] k x ∉ (A n B) <=> [x ∈ (A - B) k x ∉ (A n B)] ∨ [x ∈ (B - A) k x ∉ (A n B)] ∨ [x ∉ (A n B) k x ∉ (A n B)] <=> [x ∈ (A - B)] ∨ [x ∈ (B - A)] ∨ [x ∉ o] <=> x ∈ (A - B) ∨ x ∈ (B - A) <=> x ∈ [(A - B) u x ∈ (B - A)]