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

theorem
  a < b & c <= d implies a-d < b-c
proof
  assume
A1: a < b;
  assume c <= d;
  then -d <= -c by Lm14;
  then a+-d < b+-c by A1,Lm8;
  hence thesis;
end;
