set courses;

param totaldays:= 6;

set days;

param grade {n in courses, i in days};

set states{n in courses}:=
if n=1 then 6
	else 6-(n-1)-2 .. 6-(n-1);

set options{n in courses, d in states[n]}:=
if n=4 then d else 1..min( 3, d+n-4 );

param cumulative_grade{n in courses, d in states[n]}:=
	if n=4 then grade[n,d] else 
		max{i in options[n,d]} (grade[n,i]+ cumulative_grade[n+1,d-i]) ;

set opt{n in courses, d in states[n]: n!=4}:=
   { i in options[n,d]:
    cumulative_grade[n,d] = grade[n,i]+ cumulative_grade[n+1,d-i] };

data;

set courses:= 1 2 3 4;

set days:= 1 2 3;

param grade:
	1	2	3 :=
1 	3	5	7
2	4	5	6
3 	3	6	7
4	4	7	9 ;