Pairwisely direct sum/No direct sum/Exercise

Give an example of linear subspaces ${}U_{1},U_{2},U_{3}$ in a vector space ${}V$ such that ${}V=U_{1}+U_{2}+U_{3}$, such that ${}U_{i}\cap U_{j}=0$ for ${}i\neq j$ holds, and such that the sum is not direct.

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