Answer
$\text{(X) is a proper subset of (Y) }$$\quad \approx \quad (X \subset Y)$
$\text{This means X is a subset of Y, but X ≠ Y.}$
$\text{in other words all element of X exists in Y but The reverse is incorrect}$
See the following Venn diagram for proper subsets $ (X \subset Y)$:
Work Step by Step
$\text{(X) is a proper subset of (Y) }$$\quad \approx \quad (X \subset Y)$
$\text{This means X is a subset of Y, but X ≠ Y.}$
$\text{in other words all element of X exists in Y but The reverse is incorrect}$
See the following Venn diagram for proper subsets $ (X \subset Y)$:
