Distillation of Nat (plus minus) composition does not terminate

Distillation does not terminate for [plusMinus_1](https://github.com/YaccConstructor/Distiller/blob/draft-arch/inputs/plusMinus_1.pot) while terminates for [plusMinus_2](https://github.com/YaccConstructor/Distiller/blob/draft-arch/inputs/plusMinus_2.pot)
Branch: draft-arch
