deffunc H₁( Element of NAT ) -> Element of the carrier of X = (S . $1) * a;
ex S being sequence of X st
for n being Element of NAT holds S . n = H₁(n) from FUNCT_2:sch 4();
hence ex b₁ being sequence of X st
for n being Element of NAT holds b₁ . n = (S . n) * a ; :: thesis: verum