let s be SCM-State; :: thesis: for u being natural Number holds (SCM-Chg (s,u)) . NAT = u
let u be natural Number ; :: thesis: (SCM-Chg (s,u)) . NAT = u
NAT in dom (NAT .--> u) by TARSKI:def 1;
hence (SCM-Chg (s,u)) . NAT = (NAT .--> u) . NAT by FUNCT_4:13
.= u by FUNCOP_1:72 ;
:: thesis: verum