for P, Q being pcs-Str holds
( the carrier of (pcs-sum (P,Q)) = the carrier of P \/ the carrier of Q & the InternalRel of (pcs-sum (P,Q)) = the InternalRel of P \/ the InternalRel of Q & the ToleranceRel of (pcs-sum (P,Q)) = the ToleranceRel of P \/ the ToleranceRel of Q )