Inferring objects by number of their free attributes

[c71n93]

Example:

[x y] > obj1
  [] > attr
    x.plus y > @

[x] > obj2
  [] > attr
    x.plus 1 > @

[x] > main
  attr. > @
    x 1 2

Here x free attribute in main can be only obj1, because two free attributes are applied to it. But for now, tool can't infer objects by number of their free attributes. This functionality should be added.

[c71n93]

@yegor256 I added issue, that was discussed when I gave a seminar. But while testing this example I found some cases, that are not recognized by tool (#40 and #39). I think before the current issue, these two should be fixed. I want to start with #40, WDYT?