in reactor/Core/src/jetbrains/mps/logic/reactor/core/internal/ReteRuleMatcherImpl.kt [576:583]
fun unionNext(that: Joint) {
val prevRep = this.find()
val nextRep = that.find()
if (prevRep === nextRep) return
nextRep.rep = prevRep
nextRep.prev = nextRep
prevRep.next = nextRep.next
}