from itertools import combinations

def combinations$($k$,$ elements$)$:

assert isinstance$($elements$,$ list$)$

if k $>$ len$($elements$)$:

return set$()$

elif k $==$ len$($elements$)$:

return $\{$tuple$($elements$)\}$

elif k $==1$:

return set$(($e$,)$for e in elements$)$

else:

result $=$ set$()$

for i in range$($len$($elements$))$:

for combo in combinations$($k$,$ elements$[$i$+1$:$])$:

result.add$(($elements$[$i$],)+$ combo$)$

return result