reserve a,b,c,d for Real;
reserve r,s for Real;
reserve p,q,r,s,t for ExtReal;

theorem
 1 <= a implies a -' 1 < a
 proof
  assume 1 <= a;
  then a -' 1 = a - 1 by Th48,XREAL_0:def 2;
  hence a -' 1 < a by Th44;
 end;
