theorem
  1<=i & 1<=i1-'i implies i1-'i<i1
proof
  assume that
A1: 1<=i and
A2: 1<=i1-'i;
  i1-i=(i1-'i)+i-i by A2,Th43
    .=i1-'i;
  hence thesis by A1,XREAL_1:231;
end;
