replace support in qualitative influence line analysis

In i ) I was told that for the pinned support , we can assume to replace it with a roller , while for the cantilever , we can assume it to be supported by double roller .

For the cantilever , why we cant replace it with roller instead of double roller ? What 's the difference between double and single roller ?

In iv ) I was told that we can use roller guide , so from the figure , it's single roller , right ? So , IMO , the ii) was wrong , for the cantilever , we should always use single roller

• I've just posted an answer to your other recent question. This question looks to be along similar lines; the answer to the other question may also apply here. – AndyT Jan 23 '17 at 10:45
• Ok, @AndyT , i understand that the statement In order to draw the deflected shape properly, the capacity of the beam to resist the applied function must be removed so the beam can deflect when the function is applied. For the cantilever , why we cant replace it with roller instead of double roller ? What 's the difference between double and single roller ? – kelvinmacks Jan 23 '17 at 11:41
• continuous from previous comment , In iv ) I was told that we can use roller guide , so from the figure , it's single roller , right ? So , IMO , the ii) was wrong , for the cantilever , we should always use single roller – kelvinmacks Jan 23 '17 at 11:42
• Why we need to use double roller for case iv ? – kelvinmacks Jan 23 '17 at 11:42