for x being Variable
for H, H1 being ZF-formula st H is existential holds
( ( x = bound_in H implies ex H1 being ZF-formula st Ex (x,H1) = H ) & ( ex H1 being ZF-formula st Ex (x,H1) = H implies x = bound_in H ) & ( H1 = the_scope_of H implies ex x being Variable st Ex (x,H1) = H ) & ( ex x being Variable st Ex (x,H1) = H implies H1 = the_scope_of H ) )