theorem
 for p being PartState of S, i,j being Nat
 holds IncIC(IncIC(p,i),j) = IncIC(p,i+j)
 proof let p be PartState of S, i,j being Nat;
  thus IncIC(IncIC(p,i),j)
        = p +* Start-At(IC p+i,S) +* Start-At(IC p + i +j,S) by Th53
       .= IncIC(p,i+j) by FUNCT_4:114;
 end;
