for H being ZF-formula holds
( ( H is disjunctive implies ex F, G being ZF-formula st H = F 'or' G ) & ( ex F, G being ZF-formula st H = F 'or' G implies H is disjunctive ) & ( H is conditional implies ex F, G being ZF-formula st H = F => G ) & ( ex F, G being ZF-formula st H = F => G implies H is conditional ) & ( H is biconditional implies ex F, G being ZF-formula st H = F <=> G ) & ( ex F, G being ZF-formula st H = F <=> G implies H is biconditional ) & ( H is existential implies ex x being Variable ex H1 being ZF-formula st H = Ex (x,H1) ) & ( ex x being Variable ex H1 being ZF-formula st H = Ex (x,H1) implies H is existential ) ) ;