reserve a,b,p,k,l,m,n,s,h,i,j,t,i1,i2 for natural Number;

theorem
  i<=j implies j+k-'i=j-'i+k
proof
  assume
A1: i<=j;
  hence j+k-'i=j+k-i by NAT_1:12,XREAL_1:233
    .=j-i+k
    .=j-'i+k by A1,XREAL_1:233;
end;
