Correct typos regarding results
Optlang: Give function values a special case
Optlang: start adding validity conditions
Optlang: Prove termination for valid_value
Optlang: Rearrange definitions a little
Optlang: A lot of mess from trying to optimise
Optlang: Non-terminating function for collapsing
Optlang: Start proving termination for collaps
Optlang: Prove termination of col_funs