#Dyalog APL 16.0, 15 characters (non-competing); 15.0, 17 bytes
Dyalog APL 16.0, 15 characters (non-competing); 15.0, 17 bytes
###16.0 solution
16.0 solution
{⍵⊆⍨(⍴⍵)↑⍺/+\⍺}
Dyalog APL 16.0 adds APL2's partition primitive, ⊂
, with the glyph ⊆
.
###15.0 solution:
15.0 solution:
{(-⍺)↑¨(+\⍺)↑¨⊂⍵}