minimum spanning tree lua HPPL

[Albert Chan]

It seems XCas already has "safe" extend built-in, called semi-augment

semi_augment(A,B) := when(len(A)!=len(B), extend(A,B), extend(append(A,head(B)),tail(B)))

Cas> semi_augment([[1,2],[3,6],[6,10]] , [[2,1],[6,3],[10,6]])

[[1,2], [3,6], [6,10], [2,1], [6,3], [10,6]]       // 3+3 = 6 items

Cas> semi_augment([[1,2]] , [[3,4,5]])

[[1,2], [3,4,5]]       // 1 + 1 = 2 items


Had we use extend instead, we get these:

Cas> extend([[1,2],[3,6],[6,10]] , [[2,1],[6,3],[10,6]])

[[1,2,2,1], [3,6,6,3], [6,10,10,6]]

Cas> extend([[1,2]] , [[3,4,5]])

[[1,2,3,4,5]]