reserve x for set,
  i,j,k,n for Nat,
  K for Field;
reserve a,b,c,d for Element of K;

theorem Th11:
  (the multF of K) $$ <* a,b *> = a * b
proof
  (the multF of K) $$ <* a,b *> = Product <*a,b*> by GROUP_4:def 2
    .= a * b by GROUP_4:10;
  hence thesis;
end;
