Original proof; classical forall x: Calgary TFL rules
Premise: (P and Q) -> R. Goal: P -> (Q -> R).
1 (P and Q) -> R     Premise                 open AS: none
2 P                  AS, outer block         open AS: 2
3 Q                  AS, inner block         open AS: 2,3
4 P and Q            and I 2,3               open AS: 2,3
5 R                  ->E 1,4                 open AS: 2,3
6 Q -> R             ->I 3-5                 open AS: 2
7 P -> (Q -> R)      ->I 2-6                 open AS: none
Block ranges: outer 2-6; inner 3-5.
Invalid proposed line 8: Q by reiteration from 3. Line 3 is closed.
Countervaluation to exporting Q: P=F,Q=F,R=F; premise true, Q false.