(followup to my previous letter with the same subject) I found the way to break 6.8.2 type checker. It's as easy as to uncomment Div case alternative in valueIndex. Weird. I found a solution, though. Instead of (valueIndex (x_38,(x_36,x_37))) in that Div alternative I should create expression (valueIndex x_38*valuesCount x_36*valuesCount x_37 + valueIndex x_36 * valuesCount x_37+valueIndex x_37) which is equivalent to above one. Slightly more work. And I still cannot figure why valueIndex (a,(b,c)) works in one type and doesn;t in another.