彐!and彐! 彐! a stands for xA∧vxVy(A∧SAx=y) 彐!! A stands for VnVy(A∧SAx=y) y where y is the first individual variable distinct from and all variables which occur in a Logic in Computer Science-p.6/15∃! and ∃!! ∃!xA stands for ∃xA ∧ ∀x∀y(A ∧ Sxy A ⊃ x = y) ∃!!xA stands for ∀x∀y(A ∧ Sxy A ⊃ x = y) where y is the first individual variable distinct from x and all variables which occur in A. Logic in Computer Science – p.6/15