Request: isParent?cui1,cui2

[luto65]

Dear Sirs,
I would find very useful, if there could be an API that accepts 2 CUI and then returns
a) the CUI that of the two is "predecessor"
b) if the two CUI are not along the same path, then "0"
c) if one of the two CUI is not found, then 404
d) if the two CUI are related by circularity (e.g. one is parent of the other), then 500

e.g.
Example a)
input: C0015907,C1704628
output: C1704628

Example b)
input: C1704628,C0020538
output: 0

Example c)
input: X123456,C0020538
output: 404