Let $G$ be a finite group with distinct prime divisors $p_1, p_2, \ldots, p_k$. If $Q_i$ is the Hall $p_i'$-subgroup of $G$, then the set $\sum = \{Q_1, Q_2, \ldots, Q_k\}$ is a Sylow System of $G$.
Suppose that $H\leq G$. Then $\sum \cap H := \{K \cap H \,|\, K \in \sum \}$ is not necessarily a Sylow system of $H$. I need to find a counterexample to show this.
Let $H$ be a conjugate of $Q_1$ that is not equal to $Q_1$.