reserve a,b,m,x,n,l,xi,xj for Nat,
  t,z for Integer;

theorem Th2:
  m*t >= 1 implies t >= 1
proof
  assume
A1: m*t >= 1;
  assume t < 1;
  then t <= 0 by Lm1;
  hence contradiction by A1;
end;
