Intersection on lists is not symmetric

[nvbeusekom]

It seems that the intersection operator for lists is not symmetric when it is given a list with multiple occurences.
For example:

rascal>[1,1,2] & [1,2]
list[int]: [1,1,2]

rascal>[1,2] & [1,1,2]
list[int]: [1,2]

Here the first call should actually give [1,2] since 1 only occurs once in the second list.

[jurgenvinju]

Good find! That's pretty unexpected indeed. We'll have to study a bit on how to resolve this one in an efficient manner.