fix name conflicts.
add UnionFind data structure.
implement NaryJoin logical operator.
evaluate multiway join logically.
add init for data structure folder.
do not make multiway join as default setting.
re-organize code: group rules and operators.
fix a bug, target should be first.
make MyriaAlgebra instantiable.
add hypercube optimizing.
make joined field hashable.
add repr for ZeroaryOperator.
rename join_map to conditions
add hypercube shuffle rule.
fix: first check type
fix a bug in operator test.
add unit test for nary join related rules.
fix style.
fix variable order in hyper cube.
getting correct scheme of NaryJoin.