fatal: attempt to use array `X["2"]' in a scalar context

fatal: attempt to use a scalar value as array

X[a,b,c]
X[a][b,c]
X[a][b][c]

BEGIN {
        X[1,"Jim","The quick brown fox jumps over the lazy dogs"]++;
        Y[1]["Jim","The quick brown fox jumps over the lazy dogs"]++;
        Z[1]["Jim"]["The quick brown fox jumps over the lazy dogs"]++;
        X[2,"Jack","The quick brown foxs jumps over the lazy dogs"]++;
        Y[2]["Jack","The quick brown foxs jumps over the lazy dogs"]++;
        Z[2]["Jack"]["The quick brown foxs jumps over the lazy dogs"]++;
        X[3,"Joe","The quick brown foxs jumps over the lazy dogs"]++;
        Y[3]["Joe","The quick brown foxs jumps over the lazy dogs"]++;
        Z[3]["Joe"]["The quick brown foxs jumps over the lazy dogs"]++;
      }
END {
for ( x in X )
        print x;
for ( y in Y )
        print y;
for ( z in Z )
        {
        for ( a in Z[z] )
                print z " : " a  # -> gives the error 'awk: demo.awk:20: fatal: attempt to use array `Z["1"]["Jim"]' in a scalar context' ":" Z[z][a];
        }
}

1JimThe quick brown fox jumps over the lazy dogs
2JackThe quick brown foxs jumps over the lazy dogs
3JoeThe quick brown foxs jumps over the lazy dogs
1
2
3
1 : Jim
2 : Jack
3 : Joe

Z[z][a]

fatal: attempt to use array `Z["1"]["Jim"]' in a scalar context

split(Y[1],y_bits,SUBSEP);

awk: demo.awk:14: fatal: attempt to use array `Y["1"]' in a scalar context

split(Z[1],z_bits,SUBSEP);

split(X[1],x_bits,SUBSEP);