Check that the fact does not exist, but with the data of another fact

[kanauro]

I have a fact:
AS.run << Run(size=MATCH.size,
startX=MATCH.x,
startY=MATCH.y,
configuration=MATCH.conf,
lastX=MATCH.xe,
lastY=MATCH.ye,
length=MATCH.length,
plan=MATCH.plan)
.
I want add condition (NOT(EXISTS (Run (length = MATCH.length + 1))). \ I want verify, that there no eny facts Run, which have length ofcurrent fact "Run" - 1
I know, that "MATCH.length + 1" is elligal, but how i can it another way?