Origin for each line in src/example04.red from check-in c1ddb4c814:

c1ddb4c814 2021-03-01    1: a:=sin(x);
c1ddb4c814 2021-03-01    2: b:=cos(x);
c1ddb4c814 2021-03-01    3: c:=a+b;
c1ddb4c814 2021-03-01    4: d:=c^2;
c1ddb4c814 2021-03-01    5: % derivative
c1ddb4c814 2021-03-01    6: df(d, x);
c1ddb4c814 2021-03-01    7: % manual derivative
c1ddb4c814 2021-03-01    8: 2*(a+b)*(df(a,x)+df(b,x));
c1ddb4c814 2021-03-01    9: end;