trees :: BinTreeNode :: sibling
# Other child of the parent
# `left` or `right` depends on the position of the current node against its parent
fun sibling: nullable N do
if parent == null then
return null
else if self == parent.left then
return parent.right
else if self == parent.right then
return parent.left
else
return null
end
end
lib/trees/bintree.nit:436,2--448,4