reserve a,b,c,d for Real;
reserve r,s for Real;

theorem
  1 <= a & 1 <= b implies 1 <= a*b
proof
  assume that
A1: a>=1 and
A2: b>=1;
  a*b>=b*1 by A1,A2,Lm12;
  hence thesis by A2,XXREAL_0:2;
end;
