let H be ZF-formula; :: thesis: ( H is being_equality implies H . 1 = 0 )
assume H is being_equality ; :: thesis: H . 1 = 0
then consider x, y being Variable such that
A1: H = x '=' y ;
H = <*0,x,y*> by A1, FINSEQ_1:def 10;
hence H . 1 = 0 by FINSEQ_1:45; :: thesis: verum