thus
ex a, A being set st
( ( for x, y being Variable holds
( [(x '=' y),H8(x,y)] in A & [(x 'in' y),H9(x,y)] in A ) ) & [H,a] in A & ( for H9 being ZF-formula
for a being set st [H9,a] in A holds
( ( H9 is being_equality implies a = H8( Var1 H9, Var2 H9) ) & ( H9 is being_membership implies a = H9( Var1 H9, Var2 H9) ) & ( H9 is negative implies ex b being set st
( a = H10(b) & [(the_argument_of H9),b] in A ) ) & ( H9 is conjunctive implies ex b, c being set st
( a = H7(b,c) & [(the_left_argument_of H9),b] in A & [(the_right_argument_of H9),c] in A ) ) & ( H9 is universal implies ex b being set st
( a = H11( bound_in H9,b) & [(the_scope_of H9),b] in A ) ) ) ) )
from ZF_MODEL:sch 1(); verum