import sys
input = sys.stdin.readline

T=int(input())
for tests in range(T):
    N=int(input())
    S=list(map(int,input().split()))

    X=[]
    for s in S:
        if X and X[-1]==s:
            continue
        else:
            X.append(s)

    if len(X)==len(set(X)):
        ANS=" ".join(map(str,X))
    else:
        ANS="IMPOSSIBLE"


    print("Case #"+str(tests+1)+": "+str(ANS))